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CVE-2026-56409· NVD / CVE Program· CNA mitre

xmlwf in libexpat before 2.8.2 has an integer overflow for the output filename when -d outputDir is used.

MediumCVSS 6.5 · v3.1—No exploit Fix available
Published
Jun 21, 2026
Updated
Jun 23, 2026
EPSS
0.1% · 2th percentile
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Action score

26

Monitor

Low priority for now.

CVSS
26 / 40 · 6.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · mitre
6.5
NVD has not scored this yet; the score shown is the CNA’s.

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

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 2.8.2

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

Package-level exposure

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

EcosystemPackageAffected rangeFix
Alpine:v3.21expatbefore 2.8.2-r02.8.2-r0
Debian:12expatbefore 2.5.0-1+deb12u32.5.0-1+deb12u3
Debian:13expatbefore 2.8.2-1~deb13u12.8.2-1~deb13u1
Debian:14expatbefore 2.8.2-12.8.2-1
openSUSE:Leap 16.0expatbefore 2.8.4-160000.1.12.8.4-160000.1.1
openSUSE:Tumbleweedexpatbefore 2.8.2-1.12.8.2-1.1

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-2022-25315In 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 libexpat2.8.2Vendor (CNA)
alpine:expat2.8.2-r0 · Alpine:v3.21Package registry (OSV)
debian:expat2.5.0-1+deb12u3 · Debian:12Package registry (OSV)
opensuse:expat2.8.2-1.1 · openSUSE:TumbleweedPackage 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-2026-25210142 days apartIn libexpat before 2.7.4, the doContent function does not properly determine the buffer size bufSize because there is no integer overflow ch
    31Monitor
  • CVE-2026-564030 days apartlibexpat before 2.8.2 has an integer overflow in storeAtts.
    27Monitor
  • CVE-2026-564050 days apartlibexpat before 2.8.2 has an integer overflow in getAttributeId.
    27Monitor
  • CVE-2026-564080 days apartlibexpat before 2.8.2 has an integer overflow in copyString.
    27Monitor
  • CVE-2026-564100 days apartxmlwf in libexpat before 2.8.2 has an integer overflow in resolveSystemId.
    27Monitor
  • CVE-2026-564110 days apartxmlwf in libexpat before 2.8.2 has an integer overflow in endDoctypeDecl via NOTATION declarations.
    27Monitor

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.
  • No account or password is required.
  • A user must open a link or visit a page.
  • Special conditions such as timing or configuration are required.

If successful

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

Weakness class (CWE)

CWE-190 · Integer Overflow or Wraparound

CVSS vector

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

nvd-secondary

Attack context

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

ATT&CK techniques

—

Noroxi analysis

No Noroxi analysis for this record yet

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Change log

  1. Fix✗ → ✓

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References

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

All records