Vulnerability · Published Feb 4, 2026 · Assigned by GitHub_M

CVE-2026-25541Bytes is vulnerable to integer overflow in BytesMut::reserve

Medium 5.5

In plain English

A medium-severity security flaw in bytes from tokio-rs. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 49% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code. Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)5.5Medium

Exploit odds (30 days)0.6%top 51.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack tooling1Public PoC

Official description

Bytes is a utility library for working with bytes. From version 1.2.1 to before 1.11.1, Bytes is vulnerable to integer overflow in BytesMut::reserve. In the unique reclaim path of BytesMut::reserve, if the condition "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. This issue has been patched in version 1.11.1.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	rust-bytes	no fix listed	DEBIAN-CVE-2026-25541
Debian:13	rust-bytes	no fix listed	DEBIAN-CVE-2026-25541
Debian:14	rust-bytes	1.11.1-1	DEBIAN-CVE-2026-25541
Ubuntu:22.04:LTS	rust-bytes	no fix listed	UBUNTU-CVE-2026-25541
Ubuntu:24.04:LTS	rust-bytes	no fix listed	UBUNTU-CVE-2026-25541
Ubuntu:25.10	rust-bytes	no fix listed	UBUNTU-CVE-2026-25541
Ubuntu:26.04:LTS	rust-bytes	no fix listed	UBUNTU-CVE-2026-25541

Affected products (as reported)

Vendor	Product	Versions
tokio-rs	bytes	>= 1.2.1, < 1.11.1

Weakness: CWE-680 · Vector: 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

References

https://github.com/tokio-rs/bytes/security/advisories/GHSA-434x-w66g-qw3r x_refsource_CONFIRM
https://github.com/tokio-rs/bytes/commit/d0293b0e35838123c51ca5dfdf468ecafee4398f x_refsource_MISC
https://github.com/tokio-rs/bytes/releases/tag/v1.11.1 x_refsource_MISC
https://rustsec.org/advisories/RUSTSEC-2026-0007.html x_refsource_MISC