bytes has integer overflow in BytesMut::reserve

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

5.5 · 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 · score source

EPSS

• CVE-2026-25541: 0.60% estimated exploitation activity in the next 30 days; percentile 48.82 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Details In the unique reclaim path of BytesMut::reserve, the condition uses an unchecked addition. When newcap + 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 sparecapacitymut() 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 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.

Published by the source

3 Feb 2026, 19:17 UTC

Last modified by the source

5 Feb 2026, 00:37 UTC

Source last checked

26 Oct 2026, 15:39 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-434x-w66g-qw3r

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# Patch Next advisory brief: CVE-2026-25541

Advisory: bytes has integer overflow in BytesMut::reserve
IDs: CVE-2026-25541, GHSA-434x-w66g-qw3r
Record: https://patchnext.com/advisories/cve-2026-25541 (revision 1, source checked 26 Oct 2026, 15:39 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: bytes 1.11.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io bytes: affected >= 1.2.1, < 1.11.1; fixed in 1.11.1

## Suggested inspection (read-only)
- crates.io bytes: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on bytes.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-434x-w66g-qw3r (GitHub-reviewed advisory GHSA-434x-w66g-qw3r lists affected ranges: crates.io bytes >=1.2.1 <1.11.1)

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