Skip to main content
CVE-2026-126366VulnerabilityPublished Updated

Microsoft · msgpack-java JRuby decoder allocates from declared header counts with no cap: 5-byte message forces multi-GiB OOM

Affects MicrosoftSource GCVE Database

0
Compare
Authoritative record:CVE-2026-126366· High 7.5

Not known to be exploited · CVSS 7.5 High : upgrade to 1.8.7 soon.

Data as of 15 Nov 2026, 10:23 UTC

CVSS 3.1 base score
7.5High
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (GitHub_M)CVSS 3.17.5
Patch
Available – fixed in 1.8.7
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 12 Nov 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: 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 14 Nov 2026.

What to do

Upgrade msgpack-ruby to 1.8.7.

Affected software

ProductAffectedFixed in
msgpackmsgpack-rubyAffected
  • <1.8.7
Fixed in
  • 1.8.7
RubyGemsmsgpack-rubypkg:gem/msgpack-rubyOther threatsAffected
  • <1.8.7
Fixed in
  • 1.8.7

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

A vulnerability in the msgpack-java JRuby decoder causes it to allocate memory based on declared header counts without imposing limits. This flaw allows a crafted 5-byte message to trigger multi-gigabyte out-of-memory (OOM) conditions.

References

Community reviews

Loading reviews…