CVE-2026-27820
Description
zlib is a Ruby interface for the zlib compression/decompression library. Versions 3.0.0 and below, 3.1.0, 3.1.1, 3.2.0 and 3.2.1 contain a buffer overflow vulnerability in the Zlib::GzipReader. The zstream_buffer_ungets function prepends caller-provided bytes ahead of previously produced output but fails to guarantee the backing Ruby string has enough capacity before the memmove shifts the existing data. This can lead to memory corruption when the buffer length exceeds capacity. This issue has been fixed in versions 3.0.1, 3.1.2 and 3.2.3.
Predictions
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
Vendor advisory: debian — https://security-tracker.debian.org/tracker/CVE-2026-27820
Vendor advisory: suse — https://www.suse.com/security/cve/CVE-2026-27820.html
Vendor advisory: security-advisories@github.com — https://github.com/ruby/zlib/security/advisories/GHSA-g857-hhfv-j68w
OS impact
| OS | Version | Status | Fixed in |
|---|---|---|---|
| sles | affected | | |
| debian | bookworm | affected | |
| debian | bullseye | affected | |
| debian | forky | affected | |
| debian | sid | affected | |
| debian | trixie | affected | |
Application impact
| Vendor | Product | Versions | Fixed |
|---|---|---|---|
| ruby-lang | zlib | {"endExcluding":"3.0.1"} | 3.0.1 |
References
- https://www.ruby-lang.org/en/news/2026/03/05/buffer-overflow-zlib-cve-2026-27820
- https://github.com/ruby/zlib/security/advisories/GHSA-g857-hhfv-j68w
- https://hackerone.com/reports/3467067
- https://www.suse.com/security/cve/CVE-2026-27820.html
- https://nvd.nist.gov/vuln/detail/CVE-2026-27820
- https://github.com/ruby/zlib
- https://github.com/rubysec/ruby-advisory-db/blob/master/gems/zlib/CVE-2026-27820.yml
- https://security-tracker.debian.org/tracker/CVE-2026-27820
CWEs
CWE-120 CWE-131
Verify integrity in audit chain (admin only). AS-IS.