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CVE.org (no NVD analysis yet)· CNA VulnCheck

CVE-2026-118370: libexpat through 2.9.0 Integer Overflow in storeAtts via attIndex and nPrefixes

HighCVSS 8.2 · v4.0—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 32/100)

  • 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: 0.39% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
  • Fixed version: azl3 expat 2.8.3-2 on Azure Linux 3.0 Release Notes; azl3 expat 2.9.0-1 on Azure Linux 3.0 Release Notes.

Low priority for now. Upgrade to azl3 expat 2.8.3-2 on Azure Linux 3.0 Release Notes; azl3 expat 2.9.0-1 on Azure Linux 3.0 Release Notes 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 through 2.9.0 contains a signed integer overflow vulnerability in storeAtts() in lib/xmlparse.c that allows attackers to trigger out-of-bounds writes via oversized attribute counts. Attackers can supply a multi-gigabyte document with a start tag carrying over 2^30 attributes to overflow attIndex and nPrefixes, crashing applications or corrupting heap memory.

Published
Oct 28, 2026
Updated
Nov 2, 2026
EPSS
0.3% · 33th percentile

Report tools

JSON

Action score

32

Monitor

Low priority for now.

CVSS
32 / 40 · 8.2 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.3%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · VulnCheck
8.2
NVD has not scored this yet; the score shown is the CNA’s.

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

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.

Follow CVE-2026-118370

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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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.

VendorProduct
libexpat projectlibexpat

Versions reported by the vendor

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

  • libexpat libexpat

    • up to and including 2.9.0affected · semver

Affected versions

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

  • libexpat project libexpatup to 2.9.0 inclusive

Package-level exposure

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

EcosystemPackageAffected rangeFix
Alpine:v3.21expatbefore 2.10.0-r02.10.0-r0
Debian:12expatfrom 0—
Debian:14expatbefore 2.10.0-12.10.0-1
openSUSE:Tumbleweedexpatbefore 2.10.0-1.12.10.0-1.1

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-2026-115506Oct 22, 2026 · libexpat through 2.9.0 Denial of Service via Billion Laughs Detection Delay
    34Monitor
  • ← EarlierCVE-2026-117610Oct 28, 2026 · libexpat through 2.9.0 NULL Pointer Dereference via External Entity Subparser
    32Monitor
  • Later →CVE-2026-128241Nov 13, 2026 · libexpat xmlwf through 2.10.0 Symlink Following via -d Output Directory
    16Monitor

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
azl3 expat 2.8.3-2 on Azure Linux 3.0Release NotesMicrosoft (MSRC)
azl3 expat 2.9.0-1 on Azure Linux 3.0Release NotesMicrosoft (MSRC)
alpine:expat2.10.0-r0 · Alpine:v3.21Package registry (OSV)
debian:expat2.10.0-1 · Debian:14Package registry (OSV)
opensuse:expat2.10.0-1.1 · 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.

  1. Published
  2. Fix recorded+2 d
  3. TodayNov 13, 2026+17 d
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.

Variant candidates

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

  • CVE-2026-25210271 days apartIn libexpat before 2.7.4, the doContent function does not properly determine the buffer size bufSize because there is no integer overflow…
    31Monitor
  • CVE-2026-56403129 days apartlibexpat before 2.8.2 has an integer overflow in storeAtts.
    27Monitor
  • CVE-2026-56404129 days apartlibexpat before 2.8.2 has an integer overflow in addBinding.
    27Monitor
  • CVE-2026-56405129 days apartlibexpat before 2.8.2 has an integer overflow in getAttributeId.
    27Monitor
  • CVE-2026-56407129 days apartlibexpat before 2.8.2 has an integer overflow in doProlog that is related to storeEntityValue and entity textLen.
    27Monitor
  • CVE-2026-56408129 days apartlibexpat before 2.8.2 has an integer overflow in copyString.
    27Monitor

Not on record for this CVE: public bounty program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • Special conditions such as timing or configuration are required.

If successful

Confidentiality
Integrity
Availability
Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
X

Weakness class (CWE)

CWE-190 · Integer Overflow or Wraparound

CVSS vector

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

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

—

Change log

  1. SSVC exploitation— → none
  2. Fix✗ → ✓
  3. Exploit maturity— → none

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

References

Show all references (5 more)

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

All records