CVE-2026-6654
Received Received - Intake
Double-Free and Use-After-Free in thin_vec Causes Panic

Publication date: 2026-04-20

Last updated on: 2026-04-20

Assigner: Mozilla Corporation

Description
Double-Free / Use-After-Free (UAF) in the `IntoIter::drop` and `ThinVec::clear` functions in the thin_vec crate. A panic in `ptr::drop_in_place` skips setting the length to zero.
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Meta Information
Published
2026-04-20
Last Modified
2026-04-20
Generated
2026-06-16
AI Q&A
2026-04-20
EPSS Evaluated
2026-06-15
NVD
CVE-2026-6654
EUVD
EUVD-2026-23832
Affected Vendors & Products
Showing 2 associated CPEs
Vendor Product Version / Range
mozilla thin_vec 0.2.15
mozilla thin_vec 0.2.16
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-416 The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.
CWE-415 The product calls free() twice on the same memory address.
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Detection Guidance

This vulnerability can be detected by observing crashes or panics related to the thin_vec crate, especially when dropping iterators or clearing ThinVec instances containing elements whose Drop implementations may panic.

Using Rust's nightly toolchain with Miri or AddressSanitizer (ASAN) can help detect undefined behavior, heap-use-after-free, and double free errors caused by this vulnerability.

Suggested commands include running tests or reproducing the issue under Miri or ASAN to catch memory safety violations:

  • Run tests with Miri: `cargo +nightly miri test`
  • Run tests with AddressSanitizer enabled: `RUSTFLAGS='-Z sanitizer=address' cargo +nightly test`

Monitoring logs for panics during element drop in thin_vec usage and checking for double free or use-after-free errors in runtime diagnostics can also help detect exploitation attempts.

Mitigation Strategies

The immediate mitigation step is to upgrade the thin_vec crate to version 0.2.16 or later, where the vulnerability is fixed by implementing a DropGuard pattern or pre-zeroing the length before dropping elements.

If upgrading is not immediately possible, avoid using `IntoIter::drop` or `ThinVec::clear` on collections containing elements whose Drop implementations may panic.

Review and refactor code to ensure that Drop implementations do not panic, reducing the risk of triggering the vulnerability.

Additionally, consider adding runtime checks or wrappers to safely handle panics during element drops to prevent double free or use-after-free conditions.

Executive Summary

This vulnerability involves a Double-Free or Use-After-Free (UAF) issue in the thin_vec crate, specifically in the `IntoIter::drop` and `ThinVec::clear` functions. The problem arises because a panic in the `ptr::drop_in_place` function causes the length to not be set to zero, which can lead to memory being freed twice or accessed after it has been freed.

Impact Analysis

This vulnerability can lead to memory corruption issues such as double-free or use-after-free errors. These issues can cause program crashes, unexpected behavior, or potentially allow an attacker to execute arbitrary code or escalate privileges if exploited.

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