6.5

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2024-43806

CVE-2024-43806: rustix's `rustix::fs::Dir` iterator with the `linux_raw` backend can cause memory explosion

Summary

When using rustix::fs::Dir using the linux_raw backend, it's possible for the iterator to "get stuck" when an IO error is encountered. Combined with a memory over-allocation issue in rustix::fs::Dir::read_more, this can cause quick and unbounded memory explosion (gigabytes in a few seconds if used on a hot path) and eventually lead to an OOM crash of the application.

Details

Discovery

The symptoms were initially discovered in https://github.com/imsnif/bandwhich/issues/284. That post has lots of details of our investigation. See this post and the Discord thread for details.

Diagnosis

This issue is caused by the combination of two independent bugs:

Stuck iterator

The rustix::fs::Dir iterator can fail to halt after encountering an IO error, causing the caller to be stuck in an infinite loop.

Memory over-allocation

Dir::read_more incorrectly grows the read buffer unconditionally each time it is called, regardless of necessity.

Since <Dir as Iterator>::next calls Dir::read, which in turn calls Dir::read_more, this means an IO error encountered during reading a directory can lead to rapid and unbounded growth of memory use.

PoC

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // create a directory, get a FD to it, then unlink the directory but keep the FD
    std::fs::create_dir("tmp_dir")?;
    let dir_fd = rustix::fs::openat(
        rustix::fs::CWD,
        rustix::cstr!("tmp_dir"),
        rustix::fs::OFlags::RDONLY | rustix::fs::OFlags::CLOEXEC,
        rustix::fs::Mode::empty(),
    )?;
    std::fs::remove_dir("tmp_dir")?;

    // iterator gets stuck in infinite loop and memory explodes
    rustix::fs::Dir::read_from(dir_fd)?
        // the iterator keeps returning `Some(Err(_))`, but never halts by returning `None`
        // therefore if the implementation ignores the error (or otherwise continues
        // after seeing the error instead of breaking), the loop will not halt
        .filter_map(|dirent_maybe_error| dirent_maybe_error.ok())
        .for_each(|dirent| {
            // your happy path
            println!("{dirent:?}");
        });

    Ok(())
}

Miggo Vulnerability Database

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CVE-2024-43806

CVE-2024-43806:

6.5

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
rustix	rust	>= 0.35.11, < 0.35.15	0.35.15
rustix	rust	>= 0.36.0, < 0.36.16	0.36.16
rustix	rust	>= 0.37.0, < 0.37.25	0.37.25
rustix	rust	>= 0.38.0, < 0.38.19	0.38.19

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability stems from two interconnected issues: 1) read_more's buffer growth policy allowed unlimited allocation, and 2) read's error handling didn't terminate iteration. The commit diff shows read_more originally used wild-guess resizing (vulnerable), while read lacked error state tracking. Together they created the memory explosion vector when errors occurred during directory iteration with the linux_raw backend.

Vulnerable functions

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WAF Rule

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Reasoning

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