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CVE-2026-76957· NVD / CVE Program· CNA mitre

libexpat before 2.8.4 lacks handler call depth tracking with custom encoding callbacks.

libexpat before 2.8.4 lacks handler call depth tracking with custom encoding callbacks. Thus, a use-after-free can occur. NOTE: this is similar to CVE-2026-50219, CVE-2026-56131 and CVE-2026-56412.

HighCVSS 7.8 · v3.1—No exploit Fix available
Published
Aug 20, 2026
Updated
Sep 8, 2026
EPSS
0.1% · 1th percentile
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Action score

31

Monitor

Low priority for now.

CVSS
31 / 40 · 7.8 / 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
7.8
CNA · mitre
4.9
2.9 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.

Noroxi analysis

No Noroxi analysis for this record yet

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Affected systems

VendorProduct
libexpat projectlibexpat

Affected versions

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

  • libexpat project libexpatbefore 2.8.4

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 2.8.4affected · semver

Package-level exposure

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

EcosystemPackageAffected rangeFix
Alpine:v3.21expatbefore 2.8.4-r02.8.4-r0
Debian:12expatbefore 2.5.0-1+deb12u32.5.0-1+deb12u3
Debian:13expatall versions—
Debian:14expatbefore 2.8.4-12.8.4-1
openSUSE:Leap 16.0expatbefore 2.8.4-160000.1.12.8.4-160000.1.1
openSUSE:Tumbleweedexpatbefore 2.8.4-1.12.8.4-1.1
Red Hat:hummingbird:1expatbefore 0:2.8.3-0.1.1.hum10:2.8.3-0.1.1.hum1
Red Hat:hummingbird:1expatbefore 0:2.8.4-0.1.hum10:2.8.4-0.1.hum1
Red Hat:hummingbird:1expat-develbefore 0:2.8.3-0.1.1.hum10:2.8.3-0.1.1.hum1
Red Hat:hummingbird:1expat-develbefore 0:2.8.4-0.1.hum10:2.8.4-0.1.hum1
Red Hat:hummingbird:1expat-staticbefore 0:2.8.4-0.1.hum10:2.8.4-0.1.hum1
Red Hat:hummingbird:1expat-staticbefore 0:2.8.3-0.1.1.hum10:2.8.3-0.1.1.hum1
SUSE:Linux Micro 6.2expatbefore 2.8.4-160000.1.12.8.4-160000.1.1

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.
    49Plan
  • CVE-2022-25315In Expat (aka libexpat) before 2.4.5, there is an integer overflow in storeRawNames.
    40Plan
  • CVE-2022-25235xmltok_impl.c in Expat (aka libexpat) before 2.4.5 lacks certain validation of encoding, such as checks for whether a UTF-8 character is val
    40Plan
  • 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.
    40Plan
  • CVE-2022-22824defineAttribute in xmlparse.c in Expat (aka libexpat) before 2.4.3 has an integer overflow.
    40Plan
  • CVE-2022-22823build_model in xmlparse.c in Expat (aka libexpat) before 2.4.3 has an integer overflow.
    40Plan

Remediation

Which version to upgrade to

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

Product / packageFixed versionSource
libexpat project libexpat2.8.4Vendor (CNA)
alpine:expat2.8.4-r0 · Alpine:v3.21Package registry (OSV)
debian:expat2.5.0-1+deb12u3 · Debian:12Package registry (OSV)
opensuse:expat2.8.4-1.1 · openSUSE:TumbleweedPackage registry (OSV)
red hat:expat0:2.8.3-0.1.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:expat-devel0:2.8.3-0.1.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:expat-devel0:2.8.4-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:expat-static0:2.8.3-0.1.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:expat-static0:2.8.4-0.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
suse:expat2.8.4-160000.1.1 · SUSE:Linux Micro 6.2Package 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.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

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

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

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

  • CVE-2026-5641260 days apartlibexpat before 2.8.2 does not consider XML_TOK_DATA_CHARS in doCdataSection and thus lacks handler call depth tracking for various calls fr
    23Monitor
  • CVE-2026-5021977 days apartlibexpat before 2.8.2 lacks handler call depth tracking for calls to XML_GetBuffer, XML_Parse, XML_ParseBuffer, XML_ParserFree, or XML_Parse
    23Monitor
  • CVE-2026-5613162 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

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-416 · Use After Free

CVSS vector

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

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

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

Fixed

c
lock(&dev->lock);free(dev->buf);dev->buf = NULL;unlock(&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✗ → ✓

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

References

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

All records