CVE-2025-12875: A weakness has been identified in mruby 3.4.0

Routine

MEDIUM 5.3DOWNGRADE

CVE-2025-12875 is a medium-severity flaw (CVSS 5.3) affecting mruby. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A weakness has been identified in mruby 3.4.0. This vulnerability affects the function ary_fill_exec of the file mrbgems/mruby-array-ext/src/array.c. Executing a manipulation of the argument start/length can lead to out-of-bounds write. The attack needs to be launched locally. The exploit has been made available to the public and could be used for attacks. This patch is called 93619f06dd378db6766666b30c08978311c7ec94. It is best practice to apply

Why this priority

No elevated risk signals yet

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.2% (top 93%)
CISA exploited list	No
Weakness	CWE-119, CWE-787
Published	2025-11-07
Last modified	2026-10-19

Publisher (CNA): VulDB · Vendor: mruby

Last updated 2026-10-19 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-11-07 21:15 UTCPublished CVE record published
2026-10-19 13:10 UTCUpdated Record last modified

mruby mruby DOWNGRADE

Affected: 3.4.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 3.4.0

1. Check installed version

apt-cache policy mruby || rpm -q mruby || mruby --version

2. No fixed release: DOWNGRADE to a release before 3.4.0 (Debian / Ubuntu)

apt-cache madison mruby sudo apt install mruby=<VERSION_BEFORE_3.4.0> sudo apt-mark hold mruby

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list mruby sudo dnf downgrade mruby-<VERSION_BEFORE_3.4.0> sudo dnf versionlock add mruby

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-12875?

mruby: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2025-12875 being exploited?

CVE-2025-12875 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-12875 affect?

CVE-2025-12875 affects mruby. Severity is medium (CVSS 5.3). A weakness has been identified in mruby 3.4.0. This vulnerability affects the function ary_fill_exec of the file mrbgems/mruby-array-ext/src/array.c. Executing a manipulation of the argument start/length can lead to out-of-bounds write. The

How urgent is CVE-2025-12875?

Priority 20/100. No elevated risk signals yet.

Related CVEs

CVE-2025-13120 MEDIUM 5.3 UPGRADE A vulnerability has been found in mruby up to 3.4.0
CVE-2026-1979 MEDIUM 5.3 UPGRADE A flaw has been found in mruby up to 3.4.0
CVE-2025-7207 LOW 3.3 UPGRADE A vulnerability, which was classified as problematic, was found in mruby up to 3.4.0-rc2

References

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