# CVE-2026-77299: Regexp2: Unbounded memory amplification via large `{m}` quantifier on a zero-width subexpression

Status: published. Published: 2026-11-06. Updated: 2026-11-06.

Regexp2 is a feature-rich RegExp engine for Go. Prior to version 2.3.0, when regexp2 compiles and matches a pattern containing a large fixed-count quantifier applied to a zero-width subexpression — e.g. (?:){50000000} — the match engine executes the empty loop body m-1 times, pushing two integers onto the backtracking stack on every iteration. Because the parser accepts any repetition count up to math.MaxInt32 and the backtracking stack grows without bound, a pattern of fewer than 20 bytes matched against an empty input can force multi-gigabyte allocation and OOM-kill the process. MatchTimeout does not fully mitigate this because the memory is allocated faster than the 100 ms timeout clock can fire. This issue has been patched in version 2.3.0.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- dlclark / regexp2: < 2.3.0 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 3.1: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-400, CWE-770

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/dlclark/regexp2/security/advisories/GHSA-wq9v-j77v-qr26 (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/dlclark/regexp2/commit/6e446cb3a57a0f20112bc24353604fd00bdb309a (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/dlclark/regexp2/releases/tag/v2.3.0 (CNA: GitHub_M; x_refsource_MISC)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-77299; retrieved 2026-11-06; source updated 2026-11-06

Revision: 9a736a217b19dcd38841fc9f888e5d00ca28ec2eb50a03a4e96196d9230c290a

Canonical: https://y2.dev/cve/CVE-2026-77299

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