RUSTSEC-2026-0486: xattr functions mark unwritten bytes as initialized when given a zero-length buffer
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Assessment
- Difficulty
- 2/5
- Estimated time
- 1-3 hours
- Newbie friendliness
- 62/100
Research direction
Start by checking which rustix version the project resolves: look for rustix in Cargo.toml and Cargo.lock, and run cargo tree -i rustix. The advisory says 1.1.6 is the fixed release, so the likely change is a dependency bump, for example cargo update -p rustix, and possibly a manifest edit. Run cargo build and cargo test, then confirm the lockfile shows rustix at 1.1.6 or later.
Written by the indexing model from the issue text.
Description
xattr functions mark unwritten bytes as initialized when given a zero-length buffer
| Details | |
|---|---|
| Status | unsound |
| Package | rustix |
| Version | 1.1.4 |
| URL | https://github.com/bytecodealliance/rustix/commit/8e6aaa6713d2bb64b1fdd8c472e3a32a10a76d70 |
| Date | 2026-10-27 |
The extended-attribute functions in rustix::fs (getxattr, lgetxattr, fgetxattr, listxattr, llistxattr and flistxattr) write into a Buffer and then mark as many bytes initialized as the system call reported. When the buffer has zero length, the operating system treats the call as a size query: it writes nothing and returns the size of the attribute value or of the name list. rustix still marked that many bytes as initialized.
Passing a Vec whose length equals its capacity through spare_capacity gives such a zero-length buffer, and rustix then set the vector's length past its capacity over memory that was never written. This is undefined behavior reachable from safe code. With an empty &mut [MaybeUninit<u8>] the call panics instead.
From 1.1.6 these functions return an empty result for a zero-length buffer, and new getxattr_query, lgetxattr_query, fgetxattr_query, listxattr_query, llistxattr_query and flistxattr_query functions return the size. The 0.38 series did not have the Buffer API and is not affected.
See advisory page for additional details.
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