What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-02-04 · updated 2026-06-17
• Weakness: CWE-680

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 products

• tokio-rs bytes: from 1.2.1 before 1.11.1 — fixed in 1.11.1

How to fix

Upgrade to a fixed version: tokio-rs bytes 1.11.1. Check the vendor advisory for mitigations.

References

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

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