Integer Overflow Affecting github.com/klauspost/compress/s2 package, versions >=1.16.0 <1.18.7
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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- published28 Jul 2026
- disclosed27 Jul 2026
- creditChristopher Linke
Introduced: 27 Jul 2026
CVE-2026-63209 (opens in a new tab)How to fix?
Upgrade github.com/klauspost/compress/s2 to version 1.18.7 or higher.
Overview
Affected versions of this package are vulnerable to Integer Overflow leading to an out-of-bounds write in the s2.NewDict() function in s2/dict.go, which reads a uvarint and converts it to int without checking whether it exceeds MaxInt64. An attacker can crash the process with a segmentation fault by supplying S2 dictionary data whose repeat-index uvarint exceeds MaxInt64, which becomes a negative int that bypasses the index validation and drives out-of-bounds arithmetic through unsafe.Pointer in Dict.Encode(). Exploitation requires the application to build an S2 dictionary from attacker-controlled data with s2.NewDict() and then call Dict.Encode() on input of at least 32 bytes.