tokio-rs bytes up to 1.11.0 spare_capacity_mut integer overflow

Summaryinfo

A vulnerability was found in tokio-rs bytes up to 1.11.0. It has been declared as problematic. Impacted is the function spare_capacity_mut. The manipulation results in integer overflow. This vulnerability was named CVE-2026-25541. The attack needs to be approached locally. There is no available exploit. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability classified as problematic has been found in tokio-rs bytes up to 1.11.0. Affected is the function spare_capacity_mut. The manipulation with an unknown input leads to a integer overflow vulnerability. CWE is classifying the issue as CWE-680. The 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. This is going to have an impact on availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-25541 since 02/02/2026. The exploitability is told to be easy. The attack needs to be approached locally. There are known technical details, but no exploit is available.

Upgrading to version 1.11.1 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch d0293b0e35838123c51ca5dfdf468ecafee4398f is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-5321). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Vendor

• tokio-rs

Name

• bytes

Version

• 1.0
• 1.1
• 1.2
• 1.3
• 1.4
• 1.5
• 1.6
• 1.7
• 1.8
• 1.9
• 1.10
• 1.11.0

License

• open-source

Website

• Product: https://github.com/tokio-rs/bytes/

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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