8 ms·

I'm unreasonably excited about WASI. WASI is the thing which takes WebAssembly from a tool for running stuff in a browser to a tool that can run entire portable

by simonw 5mo ago

I'm unreasonably excited about WASI. WASI is the thing which takes WebAssembly from a tool for running stuff in a browser to a tool that can run entire portable sandboxed applications on a computer - with controlled filesystem and network access. I don't ever want to run untrusted code from the internet outside of a sandbox ever again. If WASI lives up to its full potential I won't have to - we'll have a robust, cross-platform sandboxing solution for running real applications.

Panzerschrek 5mo ago
> I don't ever want to run untrusted code from the internet outside of a sandbox ever again WASM is great, but I think it's a wrong approach for sandboxing problem. It's technically possible to sandbox native applications (compiled into target machine code) using OS-builtin mechanisms, but it's not done for compatibility reasons, because this is the way things were done last 50 years or so.
- tancop 5mo ago
  sandboxing native apps just gives you security. with wasm you also get a single portable binary that can run on x86 windows, arm64 linux and in your browser with zero modification. you dont need to write platform specific code or use third party frameworks.
  - Panzerschrek 5mo ago
    > you dont need to write platform specific code You don't need to write platform-specific code if you use some cross-platform framework. For simple programs it may be enough to use only the standard library of your language of choice. > single portable binary that can run on x86 windows, arm64 linux and in your browser with zero modification It has little value. Compiling a separate binary for each OS isn't that hard, since only a handful of architectures and operating systems are actually in use. Using an abstract cross-platform binary (like WASM) in the other hand adds extra performance costs and other user-side overhead, which isn't strictly necessary.
    - zcw100 5mo ago
      > You don't need to write platform-specific code if you use some cross-platform framework. For simple programs it may be enough to use only the standard library of your language of choice. That's a circular argument and "some" is doing a lot of work there. What cross-platform framework would you be referring to? > It has little value. Compiling a separate binary for each OS isn't that hard, since only a handful of architectures and operating systems are actually in use. Using an abstract cross-platform binary (like WASM) in the other hand adds extra performance costs and other user-side overhead, which isn't strictly necessary. It my have little value to you but that doesn't mean it has little value to everyone. I don't agree that compiling to multiple architectures is without difficulty and restricting yourself to only popular ones proves the point. What specific "other user-side overhead" would you be referring to? Lots of things aren't strictly necessary, that doesn't imply they're not necessary. Yes, there is a performance cost. Sometimes that cost is worth paying.
  - pjmlp 5mo ago
    No you don't, because WASM is only compute, and you need exactly runtime specific code and third party frameworks for everything else as imported functions.
    - hmry 5mo ago
      That's what WASI is for
      - pjmlp 5mo ago
        And like CORBA, or POSIX, the portability does not work 100% as being sold.
  - deleted 5mo ago
    [deleted]
- rvz 5mo ago
  Exactly. It is entirely a misconception to believe that WASM is this silver bullet on sandboxing and it is not that great security-wise I’m afraid. It is only now being inspected by researchers and attackers who have found sandbox escapes [0] (chrome 0day), out-of-bounds [1] / use-after-free [2] and many other [3] flaws [4] in WebAssembly which I also agree that it is not enough for sandboxing at all. [0] https://nvd.nist.gov/vuln/detail/CVE-2026-11645 https://nvd.nist.gov/vuln/detail/CVE-2026-11645 [1] https://bugzilla.mozilla.org/show_bug.cgi?id=2009901 https://bugzilla.mozilla.org/show_bug.cgi?id=2009901 [2] https://bugzilla.mozilla.org/show_bug.cgi?id=2013741 https://bugzilla.mozilla.org/show_bug.cgi?id=2013741 [3] https://www.miggo.io/vulnerability-database/cve/CVE-2026-26956 https://www.miggo.io/vulnerability-database/cve/CVE-2026-269... [4] https://github.com/bytecodealliance/wasm-micro-runtime/security/advisories/GHSA-8fc8-4g25-c8m7 https://github.com/bytecodealliance/wasm-micro-runtime/secur...
  - hobofan 5mo ago
    Those are not flaws in WASM itself, but in different WASM runtimes.
    - GoblinSlayer 5mo ago
      Might as well run java or flash.
      - DonHopkins 5mo ago
        But WASM is "lawnmower not included"!
  - dns_snek 5mo ago
    There's no reason to believe that [0] has anything to do with WASM, [1] and [2] are runtime implementation bugs, [3] is a vulnerability in a "weak" sandboxing library VM2 - it has nothing to do with WASM as such, and [4] is another implementation bug in an experimental WASI feature of that specific runtime which is gated behind a build flag. ------ [Re: 3] https://github.com/patriksimek/vm2 https://github.com/patriksimek/vm2 > vm2 attempts to sandbox untrusted JavaScript code within the same Node.js process as your application. It does this through a complex network of Proxies that intercept and mediate every interaction between the sandbox and the host environment. > JavaScript is an extraordinarily dynamic language. Objects can be accessed through prototype chains, constructors can be reached via error objects, symbols provide protocol hooks, and async execution creates timing windows. The sheer number of ways to traverse from one object to another in JavaScript makes building an airtight in-process sandbox extremely difficult. [Re: 4] https://github.com/search?q=repo%3Abytecodealliance%2Fwasm-micro-runtime+uvwasi+language%3AMarkdown&type=code&l=Markdown https://github.com/search?q=repo%3Abytecodealliance%2Fwasm-m...
wyager 5mo ago
I'm curious if people have a good story for why WASI will succeed where Java failed
- simonw 5mo ago
  My main one is that WASI has benefitted from an additional 31 years of accumulated industry-wide experience compared to when Java was first released.
  - pjmlp 5mo ago
    So where has the experience gone in the support of C and C++ for WASM?
  - DonHopkins 5mo ago
    Plus, Larry Ellison doesn't own WASM: "Lawnmower Not Included"!
- Panzerschrek 5mo ago
  Programs written in Java require installation of a middleware called Java runtime. It adds extra friction for end-users. And even if one has Java runtime installed, a newer version may be necessary for a recently-published application. With WASM it may be the same, unless al major OS vendors integrate a WASM runtime so that it doesn't need to be installed separately.
  - pjmlp 5mo ago
    It is exactly the same for WASM outside of the browser, and Java has Android as counter part to built in runtime.
    - auggierose 5mo ago
      Yes, but inside the browser is a freaking big use case.
      - 5mo ago
yjftsjthsd-h 5mo ago
Hey, this is also my interest. I was just looking into whether it was possible to e.g. build an archive extractor that runs like a normal program but does the actual extraction completely in wasm. Unfortunately, AFAICT it's possible but requires custom code; you can't (yet, I hope) just compile unzip/libarchive/whatever with CC=wasicompiler and get a sandboxed binary. But we're getting close.
- nl 5mo ago
  What do you mean? You absolutely can run compression in WASM. For example here is Gzip in WASM: https://github.com/ColinTimBarndt/wasm-gzip https://github.com/ColinTimBarndt/wasm-gzip
- fc417fc802 5mo ago
  You should be able to do exactly that though? Why do you think you can't? You will of course need to include a lot of support code to provide the relevant syscalls and otherwise emulate the environment that the code expects. But there are plenty of examples of that at this point.
  - yjftsjthsd-h 5mo ago
    Yeah, it's all that support code that I don't want to write. I want to (roughly) just tar -xf unzip.tar.gz && cd unzip ./configure CC=wasmcc make wasmruntime unzip.wasm testfile.zip
DanielHB 5mo ago
Use cases I am more excited about: 1) Replace webhooks in web apps with wasm binaries provided by the customer, but that run in the web app servers. 2) Safer plugin system for professional software (plugins for photoshop, plugins for IDEs, etc) 3) Safer mod system for games and server-side mods that run on the game-maker server.
- tuananh 5mo ago
  i had this same vision when i created hyper-mcp with modular plugin system via WASM plugins. Too bad, the community moves on from MCP to CLI with coding agent https://github.com/hyper-mcp-rs/hyper-mcp https://github.com/hyper-mcp-rs/hyper-mcp
- bzzzt 5mo ago
  We had that in the 90's with Java. Why would this approach succeed today?
  - simonw 5mo ago
    Why wouldn't it? It's a different technology stack, developed with the benefit of decades of additional experience running hostile code on the web.
    - pjmlp 5mo ago
      You mean like the CLR? Kind of strange that such experience still allows for WASM to be the target of C and C++ compilers, and there is no bounds checking support inside linear memory regions.
  - dtj1123 5mo ago
    Because Java is a language, not a compilation target?
    - ptx 5mo ago
      From the introduction section of the Java specification [1]: "The Java Virtual Machine is the cornerstone of the Java platform. It is the component of the technology responsible for its hardware- and operating system-independence, the small size of its compiled code, and its ability to protect users from malicious programs." [1] https://docs.oracle.com/javase/specs/jvms/se26/html/jvms-1.html https://docs.oracle.com/javase/specs/jvms/se26/html/jvms-1.h...
emadda 5mo ago
I like the technical design of WASM, but I feel that better OS sandboxes for regular native code will be the common approach to running untrusted code. As soon as you compile to WASM you no longer have the C FFI and the ability to call the OS systems interfaces for files, network and others. It is extra work to move something to WASM vs just compiling it and running it in a sandbox.
grayrest 5mo ago
The thing that interests me the most is that execution is deterministic. If the inputs to a WASM module are logged you get durable execution and rr style reverse debugging as part of the package.
- sideeffffect 5mo ago
  If you're interested in this, then you should check out https://github.com/golemcloud/golem https://github.com/golemcloud/golem Golem is a durable workflow platform and can run any wasm.
samiv 5mo ago
Sorry but how exactly does the sandboxing help? You download and run an app that you expect to be useful and that you need. The app needs permission to access your data. If you want to use the application what choice do you have except to grant it access? Point being you wouldn't run untrusted code in the first place and for "trusted code" you end up accepting it's access requirements anyway. So logically I'd think that the malware would just get piggy bagged into actual non-obvious utility apps and nothing is gained. Second problem is that the security model hoops make for terrible APIs and user experiences. Just look at the current filesystem browser APIs. It must be mentally challenging to design APIs to Be usable and the nerf them for security purposes to make them "not too usable". Finally one must note that at least right now the webasm ecosystem is rather immature and the de-facto only tool (emscripten) is an amateur hour hobby project. So it's going to take some decades still before the tooling is really getting there.
- eviks 5mo ago
  > The app needs permission to access your data. If you want to use the application what choice do you have except to grant it access? But it doesn't need network access to be useful, so it doesn't have that permission and can't exfiltrate your data?
  - pjmlp 5mo ago
    https://learn.microsoft.com/en-us/windows/security/application-security/application-isolation/windows-sandbox/windows-sandbox-configure-using-wsb-file https://learn.microsoft.com/en-us/windows/security/applicati...
    - eviks 5mo ago
      In general, what's three point of a link to a sandbox in a conversation about the benefits of sanboxingm But specifically, this sandbox also kills all interop with your system, other apps/utilities, so way too disruptive for the purpose of isolating just from the network.
      - 5mo ago
pistoriusp 5mo ago
Why not just run a vm?
- AndrewDucker 5mo ago
  Far more overhead.
  - ptx 5mo ago
    In particular (as I just learned when looking it up), WASM can dynamically allocate host memory with the memory.grow instruction, so you don't have to waste a huge chunk of statically allocated memory per VM: https://developer.mozilla.org/en-US/docs/WebAssembly/Reference/Memory/grow https://developer.mozilla.org/en-US/docs/WebAssembly/Referen... Although... it doesn't say anything about releasing memory back to the host (I don't see a memory.shrink instruction) so maybe it's not all that helpful? Will WASM applications continue hogging the maximum amount of memory they've ever used until they're restarted? A VM could release memory back to the host using memory ballooning, but this has to be managed manually somehow, at least with QEMU.

by simonw 5mo ago

Panzerschrek 5mo ago

> I don't ever want to run untrusted code from the internet outside of a sandbox ever again WASM is great, but I think it's a wrong approach for sandboxing problem. It's technically possible to sandbox native applications (compiled into target machine code) using OS-builtin mechanisms, but it's not done for compatibility reasons, because this is the way things were done last 50 years or so.

tancop 5mo ago
sandboxing native apps just gives you security. with wasm you also get a single portable binary that can run on x86 windows, arm64 linux and in your browser with zero modification. you dont need to write platform specific code or use third party frameworks.
- Panzerschrek 5mo ago
  > you dont need to write platform specific code You don't need to write platform-specific code if you use some cross-platform framework. For simple programs it may be enough to use only the standard library of your language of choice. > single portable binary that can run on x86 windows, arm64 linux and in your browser with zero modification It has little value. Compiling a separate binary for each OS isn't that hard, since only a handful of architectures and operating systems are actually in use. Using an abstract cross-platform binary (like WASM) in the other hand adds extra performance costs and other user-side overhead, which isn't strictly necessary.
  - zcw100 5mo ago
    > You don't need to write platform-specific code if you use some cross-platform framework. For simple programs it may be enough to use only the standard library of your language of choice. That's a circular argument and "some" is doing a lot of work there. What cross-platform framework would you be referring to? > It has little value. Compiling a separate binary for each OS isn't that hard, since only a handful of architectures and operating systems are actually in use. Using an abstract cross-platform binary (like WASM) in the other hand adds extra performance costs and other user-side overhead, which isn't strictly necessary. It my have little value to you but that doesn't mean it has little value to everyone. I don't agree that compiling to multiple architectures is without difficulty and restricting yourself to only popular ones proves the point. What specific "other user-side overhead" would you be referring to? Lots of things aren't strictly necessary, that doesn't imply they're not necessary. Yes, there is a performance cost. Sometimes that cost is worth paying.
- pjmlp 5mo ago
  No you don't, because WASM is only compute, and you need exactly runtime specific code and third party frameworks for everything else as imported functions.
  - hmry 5mo ago
    That's what WASI is for
    - pjmlp 5mo ago
      And like CORBA, or POSIX, the portability does not work 100% as being sold.
- deleted 5mo ago
  [deleted]
rvz 5mo ago
Exactly. It is entirely a misconception to believe that WASM is this silver bullet on sandboxing and it is not that great security-wise I’m afraid. It is only now being inspected by researchers and attackers who have found sandbox escapes [0] (chrome 0day), out-of-bounds [1] / use-after-free [2] and many other [3] flaws [4] in WebAssembly which I also agree that it is not enough for sandboxing at all. [0] https://nvd.nist.gov/vuln/detail/CVE-2026-11645 https://nvd.nist.gov/vuln/detail/CVE-2026-11645 [1] https://bugzilla.mozilla.org/show_bug.cgi?id=2009901 https://bugzilla.mozilla.org/show_bug.cgi?id=2009901 [2] https://bugzilla.mozilla.org/show_bug.cgi?id=2013741 https://bugzilla.mozilla.org/show_bug.cgi?id=2013741 [3] https://www.miggo.io/vulnerability-database/cve/CVE-2026-26956 https://www.miggo.io/vulnerability-database/cve/CVE-2026-269... [4] https://github.com/bytecodealliance/wasm-micro-runtime/security/advisories/GHSA-8fc8-4g25-c8m7 https://github.com/bytecodealliance/wasm-micro-runtime/secur...
- hobofan 5mo ago
  Those are not flaws in WASM itself, but in different WASM runtimes.
  - GoblinSlayer 5mo ago
    Might as well run java or flash.
    - DonHopkins 5mo ago
      But WASM is "lawnmower not included"!
- dns_snek 5mo ago
  There's no reason to believe that [0] has anything to do with WASM, [1] and [2] are runtime implementation bugs, [3] is a vulnerability in a "weak" sandboxing library VM2 - it has nothing to do with WASM as such, and [4] is another implementation bug in an experimental WASI feature of that specific runtime which is gated behind a build flag. ------ [Re: 3] https://github.com/patriksimek/vm2 https://github.com/patriksimek/vm2 > vm2 attempts to sandbox untrusted JavaScript code within the same Node.js process as your application. It does this through a complex network of Proxies that intercept and mediate every interaction between the sandbox and the host environment. > JavaScript is an extraordinarily dynamic language. Objects can be accessed through prototype chains, constructors can be reached via error objects, symbols provide protocol hooks, and async execution creates timing windows. The sheer number of ways to traverse from one object to another in JavaScript makes building an airtight in-process sandbox extremely difficult. [Re: 4] https://github.com/search?q=repo%3Abytecodealliance%2Fwasm-micro-runtime+uvwasi+language%3AMarkdown&type=code&l=Markdown https://github.com/search?q=repo%3Abytecodealliance%2Fwasm-m...

wyager 5mo ago

I'm curious if people have a good story for why WASI will succeed where Java failed

simonw 5mo ago
My main one is that WASI has benefitted from an additional 31 years of accumulated industry-wide experience compared to when Java was first released.
- pjmlp 5mo ago
  So where has the experience gone in the support of C and C++ for WASM?
- DonHopkins 5mo ago
  Plus, Larry Ellison doesn't own WASM: "Lawnmower Not Included"!
Panzerschrek 5mo ago
Programs written in Java require installation of a middleware called Java runtime. It adds extra friction for end-users. And even if one has Java runtime installed, a newer version may be necessary for a recently-published application. With WASM it may be the same, unless al major OS vendors integrate a WASM runtime so that it doesn't need to be installed separately.
- pjmlp 5mo ago
  It is exactly the same for WASM outside of the browser, and Java has Android as counter part to built in runtime.
  - auggierose 5mo ago
    Yes, but inside the browser is a freaking big use case.
    - 5mo ago

yjftsjthsd-h 5mo ago

Hey, this is also my interest. I was just looking into whether it was possible to e.g. build an archive extractor that runs like a normal program but does the actual extraction completely in wasm. Unfortunately, AFAICT it's possible but requires custom code; you can't (yet, I hope) just compile unzip/libarchive/whatever with CC=wasicompiler and get a sandboxed binary. But we're getting close.

nl 5mo ago
What do you mean? You absolutely can run compression in WASM. For example here is Gzip in WASM: https://github.com/ColinTimBarndt/wasm-gzip https://github.com/ColinTimBarndt/wasm-gzip
fc417fc802 5mo ago
You should be able to do exactly that though? Why do you think you can't? You will of course need to include a lot of support code to provide the relevant syscalls and otherwise emulate the environment that the code expects. But there are plenty of examples of that at this point.
- yjftsjthsd-h 5mo ago
  Yeah, it's all that support code that I don't want to write. I want to (roughly) just tar -xf unzip.tar.gz && cd unzip ./configure CC=wasmcc make wasmruntime unzip.wasm testfile.zip

DanielHB 5mo ago

Use cases I am more excited about: 1) Replace webhooks in web apps with wasm binaries provided by the customer, but that run in the web app servers. 2) Safer plugin system for professional software (plugins for photoshop, plugins for IDEs, etc) 3) Safer mod system for games and server-side mods that run on the game-maker server.

tuananh 5mo ago
i had this same vision when i created hyper-mcp with modular plugin system via WASM plugins. Too bad, the community moves on from MCP to CLI with coding agent https://github.com/hyper-mcp-rs/hyper-mcp https://github.com/hyper-mcp-rs/hyper-mcp
bzzzt 5mo ago
We had that in the 90's with Java. Why would this approach succeed today?
- simonw 5mo ago
  Why wouldn't it? It's a different technology stack, developed with the benefit of decades of additional experience running hostile code on the web.
  - pjmlp 5mo ago
    You mean like the CLR? Kind of strange that such experience still allows for WASM to be the target of C and C++ compilers, and there is no bounds checking support inside linear memory regions.
- dtj1123 5mo ago
  Because Java is a language, not a compilation target?
  - ptx 5mo ago
    From the introduction section of the Java specification [1]: "The Java Virtual Machine is the cornerstone of the Java platform. It is the component of the technology responsible for its hardware- and operating system-independence, the small size of its compiled code, and its ability to protect users from malicious programs." [1] https://docs.oracle.com/javase/specs/jvms/se26/html/jvms-1.html https://docs.oracle.com/javase/specs/jvms/se26/html/jvms-1.h...

emadda 5mo ago

I like the technical design of WASM, but I feel that better OS sandboxes for regular native code will be the common approach to running untrusted code. As soon as you compile to WASM you no longer have the C FFI and the ability to call the OS systems interfaces for files, network and others. It is extra work to move something to WASM vs just compiling it and running it in a sandbox.

grayrest 5mo ago

The thing that interests me the most is that execution is deterministic. If the inputs to a WASM module are logged you get durable execution and rr style reverse debugging as part of the package.

sideeffffect 5mo ago
If you're interested in this, then you should check out https://github.com/golemcloud/golem https://github.com/golemcloud/golem Golem is a durable workflow platform and can run any wasm.

samiv 5mo ago

Sorry but how exactly does the sandboxing help? You download and run an app that you expect to be useful and that you need. The app needs permission to access your data. If you want to use the application what choice do you have except to grant it access? Point being you wouldn't run untrusted code in the first place and for "trusted code" you end up accepting it's access requirements anyway. So logically I'd think that the malware would just get piggy bagged into actual non-obvious utility apps and nothing is gained. Second problem is that the security model hoops make for terrible APIs and user experiences. Just look at the current filesystem browser APIs. It must be mentally challenging to design APIs to Be usable and the nerf them for security purposes to make them "not too usable". Finally one must note that at least right now the webasm ecosystem is rather immature and the de-facto only tool (emscripten) is an amateur hour hobby project. So it's going to take some decades still before the tooling is really getting there.

eviks 5mo ago
> The app needs permission to access your data. If you want to use the application what choice do you have except to grant it access? But it doesn't need network access to be useful, so it doesn't have that permission and can't exfiltrate your data?
- pjmlp 5mo ago
  https://learn.microsoft.com/en-us/windows/security/application-security/application-isolation/windows-sandbox/windows-sandbox-configure-using-wsb-file https://learn.microsoft.com/en-us/windows/security/applicati...
  - eviks 5mo ago
    In general, what's three point of a link to a sandbox in a conversation about the benefits of sanboxingm But specifically, this sandbox also kills all interop with your system, other apps/utilities, so way too disruptive for the purpose of isolating just from the network.
    - 5mo ago

pistoriusp 5mo ago

Why not just run a vm?

AndrewDucker 5mo ago
Far more overhead.
- ptx 5mo ago
  In particular (as I just learned when looking it up), WASM can dynamically allocate host memory with the memory.grow instruction, so you don't have to waste a huge chunk of statically allocated memory per VM: https://developer.mozilla.org/en-US/docs/WebAssembly/Reference/Memory/grow https://developer.mozilla.org/en-US/docs/WebAssembly/Referen... Although... it doesn't say anything about releasing memory back to the host (I don't see a memory.shrink instruction) so maybe it's not all that helpful? Will WASM applications continue hogging the maximum amount of memory they've ever used until they're restarted? A VM could release memory back to the host using memory ballooning, but this has to be managed manually somehow, at least with QEMU.