CVE-2026-76956: In libexpat 2.8.2 and 2.8.3 before 2.8.4, misinterpretation of getentropy's return code leads to insufficient

Routine

MEDIUM 5.9REMOTEUPGRADE

CVE-2026-76956 is a medium-severity flaw (CVSS 5.9) affecting libexpat. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In libexpat 2.8.2 and 2.8.3 before 2.8.4, misinterpretation of getentropy's return code leads to insufficient entropy, which results in being vulnerable to hash flooding attacks, causing a denial of service via crafted XML content.

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 79%)
CISA exploited list	No
Weakness	CWE-394
Published	2026-08-20
Last modified	2026-09-08

Publisher (CNA): MITRE · Vendor: libexpat project

Last updated 2026-09-08 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-20 05:16 UTCPublished CVE record published
2026-09-08 21:08 UTCUpdated Record last modified

libexpat project libexpat UPGRADE

Affected: >= 2.8.2 and < 2.8.4

Fixed in: 2.8.4

Safe to downgrade to: a release before 2.8.2

1. Check installed version

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

2. UPGRADE to 2.8.4 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade libexpat

Note

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

3. If no update is available yet, DOWNGRADE to a release before 2.8.2 (Debian / Ubuntu)

apt-cache madison libexpat sudo apt install libexpat=<VERSION_BEFORE_2.8.2> sudo apt-mark hold libexpat

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list libexpat sudo dnf downgrade libexpat-<VERSION_BEFORE_2.8.2> sudo dnf versionlock add libexpat

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-2026-76956?

libexpat: upgrade to 2.8.4. Exact commands for each OS are on this page.

Is CVE-2026-76956 being exploited?

CVE-2026-76956 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-2026-76956 affect?

CVE-2026-76956 affects libexpat. Severity is medium (CVSS 5.9). In libexpat 2.8.2 and 2.8.3 before 2.8.4, misinterpretation of getentropy's return code leads to insufficient entropy, which results in being vulnerable to hash flooding attacks, causing a denial of service via crafted XML content.

How urgent is CVE-2026-76956?

Priority 31/100. Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-56132 MEDIUM 6.9 UPGRADE In libexpat before 2.8.2, there is a heap-based buffer overflow in doProlog in xmlparse.c because scaffold bac
CVE-2026-56131 MEDIUM 4.9 UPGRADE libexpat before 2.8.2 lacks handler call depth tracking for calls to XML_ResumeParser from within handlers in
CVE-2026-56403 MEDIUM 6.9 UPGRADE libexpat before 2.8.2 has an integer overflow in storeAtts.
CVE-2026-56406 MEDIUM 6.9 UPGRADE libexpat before 2.8.2 has an integer overflow in XML_ParseBuffer because it lacked a check that was present in
CVE-2026-56407 MEDIUM 6.9 UPGRADE libexpat before 2.8.2 has an integer overflow in doProlog that is related to storeEntityValue and entity textL

References

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