CVE-2026-86138: In libxml2 before 2.15.4, xmlDictAddQString in dict.c has an integer overflow and resultant heap-based buffer

Q: How do I fix CVE-2026-86138?

libxml2: upgrade to 2.15.4. Exact commands for each OS are on this page.

Q: Is CVE-2026-86138 being exploited?

CVE-2026-86138 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-86138 affect?

CVE-2026-86138 affects libxml2. Severity is medium (CVSS 6.9). In libxml2 before 2.15.4, xmlDictAddQString in dict.c has an integer overflow and resultant heap-based buffer overflow.

Q: How urgent is CVE-2026-86138?

Priority 25/100. No elevated risk signals yet.

Routine

MEDIUM 6.9UPGRADE

CVE-2026-86138 is a medium-severity flaw (CVSS 6.9) affecting libxml2. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In libxml2 before 2.15.4, xmlDictAddQString in dict.c has an integer overflow and resultant heap-based buffer overflow.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.9 (Medium)
Attack vector	Local
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.1% (top 97%)
CISA exploited list	No
Weakness	CWE-190
Published	2026-09-05
Last modified	2026-09-15

Publisher (CNA): MITRE · Vendor: xmlsoft

Last updated 2026-09-15 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-05 05:17 UTCPublished CVE record published
2026-09-15 19:40 UTCUpdated Record last modified

xmlsoft libxml2 UPGRADE

Affected: < 2.15.4

Fixed in: 2.15.4

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy libxml2 || rpm -q libxml2 || libxml2 --version

2. UPGRADE to 2.15.4 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade libxml2

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade libxml2

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Advisories and coverage

Official advisories

Amazon Linux 2 ALAS: ALAS2-2026-3940 (medium): libxml2 2026-09-28

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-2026-86138?

libxml2: upgrade to 2.15.4. Exact commands for each OS are on this page.

Is CVE-2026-86138 being exploited?

CVE-2026-86138 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-2026-86138 affect?

CVE-2026-86138 affects libxml2. Severity is medium (CVSS 6.9). In libxml2 before 2.15.4, xmlDictAddQString in dict.c has an integer overflow and resultant heap-based buffer overflow.

How urgent is CVE-2026-86138?

Priority 25/100. No elevated risk signals yet.

Software pages

libxml2 vulnerabilities

Related CVEs

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CVE-2026-86139 MEDIUM 6.9 UPGRADE In libxml2 before 2.15.4, xmlURIEscapeStr in uri.c has an integer overflow.

References

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