CVE-2026-25541: tokio-rs bytes Integer Overflow to Buffer Overflow

Vulnerability summary

CVE-2026-25541 is a high (CVSS 7.5) Integer Overflow to Buffer Overflow vulnerability in tokio-rs bytes. EPSS estimates a 0.61% chance of exploitation in the next 30 days, higher than 48.4% of scored vulnerabilities. 2 public exploits are recorded.

Timeline

1. 04-02-2026
   PublishedVulnerability first disclosed.
2. 05-02-2026
   Last modifiedVulnerability information updated.

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.

• CWE-680Integer Overflow to Buffer OverflowThe product performs a calculation to determine how much memory to allocate, but an integer overflow can occur that causes less memory to be allocated than expected, leading to a buffer overflow.