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Vulnerabilities

Vulnerability · CVE-2026-27820

zlib is a Ruby interface for the zlib compression/decompression library.

Published Apr 16, 2026 · catalog updated Jun 17, 2026 · zlib is a Ruby

Check if you run it

No confirmed exploitation is on record for CVE-2026-27820. EPSS is 0.75%. Act only if a listed version of zlib is a Ruby is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (zlib is a Ruby).
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Low1.7
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.75%
Remediation
Advisory link
Affected products
cpe ruby-lang/zlib

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe ruby-lang/zlibversion unspecified

How to fix CVE-2026-27820

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-27820. EPSS is 0.75%. Act only if a listed version of zlib is a Ruby is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-120: Classic Buffer Overflow; CWE-131. EPSS 0.75%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Apr 16, 2026 · NIST NVD

    Detected

    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 existin

  2. Jun 17, 2026 · NIST NVD

    Updated

    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 existin

Sources

  • CVE.orgVulnerability recordCVE-2026-27820

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-27820

    30-day exploitation probability 0.8%

    first.org
  • NIST NVDVulnerability recordCVE-2026-27820

    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

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.