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VulnerabilityPublished Updated

CVE-2026-28364: Ocaml · Multiple issues in Marshal

Affects ocamlSource GCVE Database

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Not known to be exploited · CVSS 6.8 Medium : upgrade to 5.5.2 or 4.14.5 when convenient.

Data as of 6 Nov 2026, 15:38 UTC

CVSS 3.1 base score
6.8Medium
How severe the flaw is on the 0–10 CVSS scale.
Patch
Available – fixed in 5.5.2, 4.14.5
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 23 Oct 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 6 Nov 2026.

What to do

Upgrade ocaml to 5.5.2 or 4.14.5.

Affected software

ProductAffectedFixed in
opamocamlpkg:opam/ocamlOther threatsAffected
  • 5.0.0 – 5.5.1
  • <4.14.5
  • >=5 <5.5.2
15 affected builds
Fixed in
  • 4.14.5
  • 5.5.2

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

AI-suggested

A fix is available in OCaml versions 4.14.5 and 5.5.2. Users should upgrade to these or later versions to remediate the vulnerability. The vendor recommends using the Marshal module only for communication between trusted processes and avoiding unmarshaling untrusted data. No additional mitigations are specified.

Description

Multiple issues in the OCaml Marshal module allow corrupted or malicious marshaled data to cause undefined behavior in the runtime system during unmarshaling. These issues include stale obj_counter usage, custom block size wraparound, and acceptance of forged Closure_tag metadata without validation. The vulnerability affects several OCaml versions and can lead to runtime corruption or code execution if untrusted data is unmarshaled. It is recommended to use Marshal only between trusted processes. Fixes have been merged in versions 4.14.5 and 5.5.2.

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