Medium Memory corruption

CVE-2026-117610 — libexpat through 2.9.0 NULL Pointer Dereference via External Entity Subparser

libexpat through 2.9.0 contains a NULL pointer dereference vulnerability in externalEntityInitProcessor2() in lib/xmlparse.c that mishandles the XML_TOK_NONE token from empty input. Attackers who control stream chunking can force an empty non-final first parse on an external entity subparser, causing a later parse to crash the application.

Published Oct 28, 2026 · Updated Oct 28, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: VulnCheck

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.4% (30-day exploitation probability)+6
Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.43%

ahead of 37% of scored CVEs · Oct 28, 2026

Affects

Libexpat

CVSS base

5.9

Medium · 2 source(s)

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Libexpat Libexpat).
The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Libexpat	Libexpat	≤ 2.9.0	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

High

Privileges required

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
8.2	CVSS 4.0	High	—	—	disclosure@vulncheck.com via NIST National Vulnerability Database
8.2	CVSS 4.0	High	—	—	VulnCheck via CVE Program (cve.org) e CISA ADP
5.9	CVSS 3.1	Medium	2.2	3.6	disclosure@vulncheck.com via NIST National Vulnerability Database
5.9	CVSS 3.1	Medium	—	—	VulnCheck via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H (score shown at the top: disclosure@vulncheck.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-476 · NULL Pointer Dereference

Other CVEs with this weakness →

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.

web/proxy/WAF logsnetwork IDS/IPSendpoint telemetry (EDR)crash dumps

Timeline

What happened to this CVE, newest first.

2026
Source status changed · Received → Awaiting Analysis
Oct 28, 2026 · NIST National Vulnerability Database
Affected products added · libexpat/libexpat
Oct 28, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 28, 2026
CVSS changed · 5.9
Oct 28, 2026 · NIST National Vulnerability Database
Source status changed · → Received
Oct 28, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 28, 2026 · Alertas do Telegram
CVE published
Oct 28, 2026 · VulnCheck

Source activity

Repeated readings are counted rather than listed.

1× References added · Oct 28, 2026 – Oct 28, 2026
1× Official description updated · Oct 28, 2026 – Oct 28, 2026

References

5 on the record

github.com/libexpat/libexpat/pull/1444
patch, issue-tracking, NIST National Vulnerability Database
github.com/libexpat/libexpat/commit/7b0d50e4b1d16fafd55876260701e04279a7489d
patch, NIST National Vulnerability Database
github.com/libexpat/libexpat/blob/a76b1174c1ea52abb639a4c69d52b630a8a106a2/expat
technical-description, NIST National Vulnerability Database
www.vulncheck.com/advisories/libexpat-through-2.9.0-null-pointer-dereference-via-extern
third-party-advisory, NIST National Vulnerability Database
github.com/libexpat/libexpat
product, NIST National Vulnerability Database

Elsewhere on this site

Libexpat
every CVE for this vendor

Memory corruption
same class

CWE-476
other pages naming this weakness

Related CVEs (same products)

Medium CVE-2026-118370 libexpat through 2.9.0 Integer Overflow in storeAtts via attIndex and nPrefixes 1d
High CVE-2026-115506 libexpat through 2.9.0 Denial of Service via Billion Laughs Detection Delay 6d
Medium CVE-2026-113351 libexpat 2.7.2 through 2.9.0 Denial of Service via XML_ParserReset 9d
High CVE-2026-77214 libexpat Heap Buffer Over-read in xmlparse.c via XML_ParseBuffer 22d
Medium CVE-2026-102633 libexpat 2.7.2 through 2.8.5 Integer Overflow in expat_realloc Sep 29, 2026
High CVE-2026-93990 Expat before 2.8.5 Malformed UTF-16 Acceptance via Unchecked Surrogate Sep 19, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No fixed version, patch or mitigation documented.
No CISA SSVC assessment.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-117610 is "libexpat through 2.9.0 NULL Pointer Dereference via External Entity Subparser", rated Medium. It affects Libexpat (Libexpat); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.9 describes technical severity. EPSS 0.43% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

Comments

Moderated technical discussion. Read the community guidelines.

No comments yet.