NVD / CVE Program· CNA mitre

CVE-2026-56412: libexpat before 2.8.2 does not consider XML_TOK_DATA_CHARS in doCdataSection and thus lacks handler call depth tracking for various calls…

MediumCVSS 5.9 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 23/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.19% (FIRST EPSS).
Someone with local access to the system can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
Fixed version: libexpat project libexpat 2.8.2; azl3 expat 2.6.4-6 on Azure Linux 3.0 2.8.2-1.

Low priority for now. Upgrade to libexpat project libexpat 2.8.2; azl3 expat 2.6.4-6 on Azure Linux 3.0 2.8.2-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

libexpat before 2.8.2 does not consider XML_TOK_DATA_CHARS in doCdataSection and thus lacks handler call depth tracking for various calls from within handlers in cases of a policy violation. Thus, a use-after-free can occur. NOTE: this issue exists because of an incomplete fix for CVE-2026-50219.

Memory safety

Published: Jun 21, 2026
Updated: Nov 10, 2026
EPSS: 0.1% · 9th percentile
CWE: CWE-416

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 23 / 40 · 5.9 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.1%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 5.9
CNA · mitre: 4.9; 1.0 point gap

CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

If any of these changes, we'll tell you in the daily email digest.

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
libexpat project	libexpat	cpe:2.3:a:libexpat_project:libexpat

Versions reported by the vendor

Affected version ranges reported by the assigning authority (mitre). Independent of NVD's CPE analysis and usually ahead of it.

libexpat project libexpat
- before 2.8.2affected · semver

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

libexpat project libexpatbefore 2.8.2

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Alpine:v3.21	expat	before 2.8.2-r0	2.8.2-r0
Debian:12	expat	before 2.5.0-1+deb12u3	2.5.0-1+deb12u3
Debian:13	expat	before 2.8.2-1~deb13u1	2.8.2-1~deb13u1
Debian:14	expat	before 2.8.2-1	2.8.2-1
openSUSE:Leap 16.0	expat	before 2.8.4-160000.1.1	2.8.4-160000.1.1
openSUSE:Tumbleweed	expat	before 2.8.2-1.1	2.8.2-1.1
SUSE:Linux Micro 6.2	expat	before 2.8.4-160000.1.1	2.8.4-160000.1.1

Same product

libexpat project: all records

Other highest-scoring records for the same primary product.

CVE-2022-25236xmlparse.c in Expat (aka libexpat) before 2.4.5 allows attackers to insert namespace-separator characters into namespace URIs.
50Plan
CVE-2022-23852Expat (aka libexpat) before 2.4.4 has a signed integer overflow in XML_GetBuffer, for configurations with a nonzero XML_CONTEXT_BYTES.
41Plan
CVE-2022-22822addBinding in xmlparse.c in Expat (aka libexpat) before 2.4.3 has an integer overflow.
41Plan

Published before and after this one in the same product

← EarlierCVE-2026-56410Jun 21, 2026 · xmlwf in libexpat before 2.8.2 has an integer overflow in resolveSystemId.
27Monitor
← EarlierCVE-2026-56411Jun 21, 2026 · xmlwf in libexpat before 2.8.2 has an integer overflow in endDoctypeDecl via NOTATION declarations.
27Monitor
Later →CVE-2026-72522Aug 10, 2026 · libexpat before 2.8.3 has an out-of-bounds read and resultant infinite loop because low surrogates are treated the same as high surrogates…
24Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
libexpat project libexpat	2.8.2	Vendor (CNA)
azl3 expat 2.6.4-6 on Azure Linux 3.0	2.8.2-1 · CBL-Mariner Releases	Microsoft (MSRC)
alpine:expat	2.8.2-r0 · Alpine:v3.21	Package registry (OSV)
debian:expat	2.5.0-1+deb12u3 · Debian:12	Package registry (OSV)
opensuse:expat	2.8.2-1.1 · openSUSE:Tumbleweed	Package registry (OSV)
suse:expat	2.8.4-160000.1.1 · SUSE:Linux Micro 6.2	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

libexpat/libexpatPR 1278

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

CVE-2026-7695760 days apartlibexpat before 2.8.4 lacks handler call depth tracking with custom encoding callbacks.
31Monitor
CVE-2026-5021917 days apartlibexpat before 2.8.2 lacks handler call depth tracking for calls to XML_GetBuffer, XML_Parse, XML_ParseBuffer, XML_ParserFree, or…
23Monitor
CVE-2026-561312 days apartlibexpat before 2.8.2 lacks handler call depth tracking for calls to XML_ResumeParser from within handlers in cases of a policy violation.
19Monitor

Not on record for this CVE: EPSS history · researcher credit · public bounty program.

Technical details

Attack conditions

Someone with local access to the system can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: low · data can be read
Integrity: low · data or configuration can be modified
Availability: low · the service can be disrupted

Attack vector: Local
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: Low
Integrity impact: Low
Availability impact: Low

Weakness class (CWE)

CWE-416 · Use After Free

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

nvd-primary

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

The bug in code

The whole CWE-416 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1free(dev->buf);
2/* ... another thread is still running ... */
3process(dev->buf);

Fixed

1lock(&dev->lock);
2free(dev->buf);
3dev->buf = NULL;
4unlock(&dev->lock);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log (1)

Fix✗ → ✓Sep 28, 2026, 10:09 PM UTC

For records you follow, these changes also arrive as notifications. →

References

github.com/libexpat/libexpat/pull/1278

Show all references (1 more)

cert-portal.siemens.com/productcert/html/ssa-457936.html

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

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