Vulnerability 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.
CVSS Score
CRITICAL
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Ruby-Lang | Zlib | < 3.0.1 |
Related Weaknesses (CWE)
References
- https://github.com/ruby/zlib/security/advisories/GHSA-g857-hhfv-j68wVendor Advisory
- https://hackerone.com/reports/3467067Permissions Required
FAQ
What is CVE-2026-27820?
CVE-2026-27820 is a vulnerability with a CVSS score of 9.8 (CRITICAL). 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 zs...
How severe is CVE-2026-27820?
CVE-2026-27820 has been rated CRITICAL with a CVSS base score of 9.8/10. This is considered a critical vulnerability requiring immediate attention.
Is there a patch for CVE-2026-27820?
Check the references section above for vendor advisories and patch information. Affected products include: Ruby-Lang Zlib.