{"id":"GHSA-434x-w66g-qw3r","summary":"bytes has integer overflow in BytesMut::reserve","details":"# Details\n\nIn the unique reclaim path of `BytesMut::reserve`, the condition\n```rs\nif v_capacity \u003e= new_cap + offset\n```\nuses an unchecked addition. When `new_cap + offset` overflows `usize` in release builds, this condition may incorrectly pass, causing `self.cap` to be set to a value that exceeds the actual allocated capacity. Subsequent APIs such as `spare_capacity_mut()` then trust this corrupted `cap` value and may create out-of-bounds slices, leading to UB.\n\nThis behavior is observable in release builds (integer overflow wraps), whereas debug builds panic due to overflow checks.\n\n## PoC\n\n```rs\nuse bytes::*;\n\nfn main() {\n    let mut a = BytesMut::from(&b\"hello world\"[..]);\n    let mut b = a.split_off(5);\n\n    // Ensure b becomes the unique owner of the backing storage\n    drop(a);\n\n    // Trigger overflow in new_cap + offset inside reserve\n    b.reserve(usize::MAX - 6);\n\n    // This call relies on the corrupted cap and may cause UB & HBO\n    b.put_u8(b'h');\n}\n```\n\n# Workarounds\n\nUsers of `BytesMut::reserve` are only affected if integer overflow checks are configured to wrap. When integer overflow is configured to panic, this issue does not apply.\n\nThis vulnerability is also known as [RUSTSEC-2026-0007](https://rustsec.org/advisories/RUSTSEC-2026-0007.html).","aliases":["CVE-2026-25541","RUSTSEC-2026-0007"],"modified":"2026-07-17T21:08:29.851239327Z","published":"2026-02-03T19:17:46Z","database_specific":{"nvd_published_at":"2026-02-04T22:16:00Z","cwe_ids":["CWE-680"],"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2026-02-03T19:17:46Z"},"references":[{"type":"WEB","url":"https://github.com/tokio-rs/bytes/security/advisories/GHSA-434x-w66g-qw3r"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-25541"},{"type":"WEB","url":"https://github.com/tokio-rs/bytes/commit/d0293b0e35838123c51ca5dfdf468ecafee4398f"},{"type":"PACKAGE","url":"https://github.com/tokio-rs/bytes"},{"type":"WEB","url":"https://github.com/tokio-rs/bytes/releases/tag/v1.11.1"},{"type":"WEB","url":"https://rustsec.org/advisories/RUSTSEC-2026-0007.html"}],"affected":[{"package":{"name":"bytes","ecosystem":"crates.io","purl":"pkg:cargo/bytes"},"ranges":[{"type":"SEMVER","events":[{"introduced":"1.2.1"},{"fixed":"1.11.1"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/02/GHSA-434x-w66g-qw3r/GHSA-434x-w66g-qw3r.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:P"}]}