GHSA-434X-W66G-QW3R

Vulnerability from github – Published: 2026-02-03 19:17 – Updated: 2026-02-05 00:37
VLAI?
Summary
bytes has integer overflow in BytesMut::reserve
Details

Details

In the unique reclaim path of BytesMut::reserve, the condition

if v_capacity >= new_cap + offset

uses 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.

This behavior is observable in release builds (integer overflow wraps), whereas debug builds panic due to overflow checks.

PoC

use bytes::*;

fn main() {
    let mut a = BytesMut::from(&b"hello world"[..]);
    let mut b = a.split_off(5);

    // Ensure b becomes the unique owner of the backing storage
    drop(a);

    // Trigger overflow in new_cap + offset inside reserve
    b.reserve(usize::MAX - 6);

    // This call relies on the corrupted cap and may cause UB & HBO
    b.put_u8(b'h');
}

Workarounds

Users 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.

This vulnerability is also known as RUSTSEC-2026-0007.

Severity ?
5.5 (Medium)
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
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{
  "affected": [
    {
      "package": {
        "ecosystem": "crates.io",
        "name": "bytes"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.2.1"
            },
            {
              "fixed": "1.11.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-25541"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-680"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-02-03T19:17:46Z",
    "nvd_published_at": "2026-02-04T22:16:00Z",
    "severity": "MODERATE"
  },
  "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(\u0026b\"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 \u0026 HBO\n    b.put_u8(b\u0027h\u0027);\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).",
  "id": "GHSA-434x-w66g-qw3r",
  "modified": "2026-02-05T00:37:18Z",
  "published": "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"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "bytes has integer overflow in BytesMut::reserve"
}


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