CVE-2026-1979Public exploit

Interpreter crash via corrupted pattern-matching bytecode

Published Feb 6, 2026 · Updated Feb 6, 2026

Heap use-after-free in mruby 3.0 through 3.4.0 allows local users to crash the interpreter with crafted Ruby code. The pattern-matching compiler treats a three-byte OP_JMP for an undefined pinned variable as a four-byte OP_JMPNOT, corrupting a preceding bytecode operand and leaving mrb_vm_exec to read freed memory. Exploitation requires local ability to submit Ruby source to a build containing the rational and bigint extensions; the demonstrated consequence is interpreter termination.

CVSS severity5.5
Medium
EPSS probability0.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap use-after-free in mruby 3.0 through 3.4.0 allows local users to crash the interpreter with crafted Ruby code. The pattern-matching compiler treats a three-byte OP_JMP for an undefined pinned variable as a four-byte OP_JMPNOT, corrupting a preceding bytecode operand and leaving mrb_vm_exec to read freed memory. Exploitation requires local ability to submit Ruby source to a build containing the rational and bigint extensions; the demonstrated consequence is interpreter termination.

The record

CVE
CVE-2026-1979
Published
Feb 6, 2026
Updated
Feb 6, 2026
Vendor
mruby
Product
mruby
Classifications
CWE-416, CWE-119
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 6, 2026CVE publishedPublication date reported by the CVE source.
  2. Feb 6, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=3.0
  2. Affected versionversion=3.1
  3. Affected versionversion=3.2
  4. Affected versionversion=3.3
  5. Affected versionversion=3.4.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

mruby · mrubyversion=3.0; version=3.1; version=3.2; version=3.3; version=3.4.0

Published CVSS scores

1.9VulDBCVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:P
5.3VulDBCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
4.3VulDBAV:L/AC:L/Au:S/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-416Use After Free
CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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