CVE-2026-6654

Modified Modified - Updated After Analysis

Double-Free and Use-After-Free in thin_vec Causes Panic

Publication date: 2026-04-20

Last updated on: 2026-06-30

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.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-04-20

Last Modified

2026-06-30

Generated

2026-07-06

AI Q&A

2026-04-20

EPSS Evaluated

2026-07-05

NVD

CVE-2026-6654

EUVD

EUVD-2026-23832

Affected Vendors & Products

Vendor	Product	Version / Range
mozilla	thin_vec	0.2.15
mozilla	thin_vec	0.2.16

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-415	The product calls free() twice on the same memory address.
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 Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.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-1341	The product attempts to close or release a resource or handle more than once, without any successful open between the close operations.

Attack-Flow Graph

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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