klauspost compress up to 1.18.6 Dictionary s2.NewDict integer overflow

Summaryinfo

A vulnerability has been found in klauspost compress up to 1.18.6 and classified as problematic. Affected is the function s2.NewDict of the component Dictionary. This manipulation causes integer overflow. This vulnerability is handled as CVE-2026-63209. The attack can be initiated remotely. There is not any exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability has been found in klauspost compress up to 1.18.6 and classified as problematic. Affected by this vulnerability is the function s2.NewDict of the component Dictionary. The manipulation with an unknown input leads to a integer overflow vulnerability. The CWE definition for the vulnerability is CWE-190. The product performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control. As an impact it is known to affect availability. The summary by CVE is:

compress provides various compression algorithms. Prior to version 1.18.7, a signed integer overflow vulnerability in s2.NewDict() allows an attacker to bypass repeat index validation by supplying a dictionary with a uvarint-encoded repeat value exceeding MaxInt64. When Dict.Encode() is subsequently called, the overflowed negative repeat value causes an out-of-bounds memory access via unsafe.Pointer arithmetic, crashing the process with SIGSEGV. This issue has been patched in version 1.18.7.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-63209 since 07/16/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details are known, but no exploit is available.

Upgrading to version 1.18.7 eliminates this vulnerability.

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Productinfo

Vendor

• klauspost

Name

• compress

Version

• 1.18.0
• 1.18.1
• 1.18.2
• 1.18.3
• 1.18.4
• 1.18.5
• 1.18.6

Website

• Product: https://github.com/klauspost/compress/

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