CVE-2026-63209 · GHSA-259r-337f-4rfw

Compress/s2: Integer Overflow or Wraparound and Out-of-bounds Write in compress

Risk score: 61/100
CVSS: 7.5 v3.1
Exploit chance (30 days): 0.4%
Published: 29 Sep 2026

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What to know

What it 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 overfl…
Affected: github.com/klauspost/compress (go) <= 1.18.6
Fix: Upgrade github.com/klauspost/compress to 1.18.7 or later.
Exploitation: No known exploitation

Why it is Amber

CVSS 7.5 high
Remotely exploitable without logging in
On your watchlist: Go

Affected packages

Package	Ecosystem	Vulnerable	Fixed in
github.com/klauspost/compress	go	<= 1.18.6	1.18.7

References

Original description

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.

Last activity 29 Sep 2026. Patch Forecast updates every hour.