Summary
use-after-free in tracing
The implementation of the Instrumented::into_inner method in affected versions of this crate contains undefined behavior due to incorrect use of std::mem::forget The function creates *const pointers to self, calls mem::forget(self), and then moves values out of those pointers using std::ptr::read.
// To manually destructure `Instrumented` without `Drop`, we
// move it into a ManuallyDrop and use pointers to its fields
let span: *const Span = &this.span;
let inner: *const ManuallyDrop<T> = &this.inner;
mem::forget(self);
// SAFETY: Those pointers are valid for reads, because `Drop` didn't
// run, and properly aligned, because `Instrumented` isn't
// `#[repr(packed)]`.
let _span = unsafe { span.read() };
let inner = unsafe { inner.read() };
However, the mem::forget documentation states:
Any resources the value manages, such as heap memory or a file handle, will
linger forever in an unreachable state. However, it does not guarantee that
pointers to this memory will remain valid.
This means that these pointers are no longer valid. This could result in a stack use-after-free if LLVM chooses to reuse self's stack slot for a rebinding after the call to std::mem::forget.
This undefined behavior has not been observed to cause miscompilation as of Rust 1.73.0. However, any use of this method with the affected versions of tracing are unsound.
The flaw was corrected in commit 20a1762 (PR #2765) by replacing the use of std::mem::forget with std::mem::ManuallyDrop, ensuring that the stack slot is not reused and the pointers remain valid when they are read. The fix is
published in tracing v0.1.40. Affected versions have been yanked from crates.io.
Thanks to Taylor Cramer and Manish Goregaokar for finding and correcting
this issue!
Impact
Memory is accessed after it has been freed, leading to undefined behavior in native code. Typical impact: memory corruption, crash, or potential code execution.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Frequently Asked Questions
- What is GHSA-8F24-6M29-WM2R? GHSA-8F24-6M29-WM2R is a medium-severity use after free vulnerability in tracing (rust), affecting versions >= 0.1.38, < 0.1.40. It is fixed in 0.1.40. Memory is accessed after it has been freed, leading to undefined behavior in native code.
- Which versions of tracing are affected by GHSA-8F24-6M29-WM2R? tracing (rust) versions >= 0.1.38, < 0.1.40 is affected.
- Is there a fix for GHSA-8F24-6M29-WM2R? Yes. GHSA-8F24-6M29-WM2R is fixed in 0.1.40. Upgrade to this version or later.
- Is GHSA-8F24-6M29-WM2R exploitable, and should I be worried? Whether GHSA-8F24-6M29-WM2R is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether GHSA-8F24-6M29-WM2R is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix GHSA-8F24-6M29-WM2R? Upgrade
tracingto 0.1.40 or later.