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CVE-2026-27820VulnerabilityPublished Updated

Zlib::GzipReader ungetc · zlib: Buffer Overflow

Affects MicrosoftSource GCVE Database

0
Authoritative record:CVE-2026-27820· Low 1.7

Not known to be exploited · CVSS 1.7 Low · fixed in 3.2.3 : update Microsoft when convenient.

Data as of 27 Oct 2026, 00:07 UTC

CVSS 4.0 base score
1.7Low
How severe the flaw is on the 0–10 CVSS scale.
Patch
Available – fixed in 3.2.3, 3.1.2, 3.0.1
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 16 Apr 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade zlib to 3.2.3, 3.1.2 or 3.0.1.

Affected software

ProductAffectedFixed in
rubyzlibAffected
  • >=3.2.0 <3.2.3
Fixed in
  • 3.2.3
rubyzlibAffected
  • >=3.1.0 <3.1.2
Fixed in
  • 3.1.2
rubyzlibAffected
  • <3.0.1
Fixed in
  • 3.0.1

Description

To determine the support lifecycle for your software, see the Microsoft Support Lifecycle: https://support.microsoft.com/lifecycle

References

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