libexpat before 2.8.2 has an integer overflow in addBinding
libexpat project · libexpat
6.9MediumCVSS 3.1
Recommended action
Scheduled
Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.
Patch available
Distribution package intelligence
Ubuntu vendor package status
Canonical’s release and source-package findings are shown separately from local repository availability.
8 package states
Repository candidate not checked
A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.
Ubuntu release
Source package
Vendor state
Fixed version
Evidence
Ubuntu 24.04 LTSnoble · esm-apps
libxmltok
Under evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.
Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.
1 current
CVE-2026-56404 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitylibexpat: libexpat: Arbitrary Code Execution via integer overflow in addBinding
44 known affected
The vendor explicitly identifies these products as affected by this CVE.
expat as a component of Red Hat Enterprise Linux 10
expat-devel as a component of Red Hat Enterprise Linux 10
expat.src as a component of Red Hat Enterprise Linux 10
firefox as a component of Red Hat Enterprise Linux 10
firefox.src as a component of Red Hat Enterprise Linux 10
thunderbird as a component of Red Hat Enterprise Linux 10
thunderbird.src as a component of Red Hat Enterprise Linux 10
compat-expat1 as a component of Red Hat Enterprise Linux 6
compat-expat1.src as a component of Red Hat Enterprise Linux 6
expat as a component of Red Hat Enterprise Linux 6
expat-devel as a component of Red Hat Enterprise Linux 6
expat.src as a component of Red Hat Enterprise Linux 6
Summary
A flaw was found in libexpat. This vulnerability, an integer overflow in the `addBinding` function, could allow a local attacker to execute arbitrary code. By exploiting this, an attacker could gain control over the affected system, compromising its confidentiality and integrity.
Remediation
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
Optional official sources
National CERT insights ?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.
Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.
Official European source
ENISA European Vulnerability Database
Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.
1 current
ENISA EUVD identifier
EUVD-2026-38181
No EUVD known-exploited evidence
ENISA has published the identifier mapping but no EUVD description has been stored yet.
EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionScheduled
Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.
Patch available
01
What, why and how
libexpat before 2.8.2 has an integer overflow in addBinding.
What
libexpat before 2.8.2 has an integer overflow in addBinding.
Why
The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.
How
An attacker operating through local access may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
What
libexpat before 2.8.2 has an integer overflow in addBinding.
Why
The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.
How
An attacker operating through local access may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation ?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No confirmed evidence
No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.
Public PoC / exploit material ?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.None recorded
No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.
Likely attack path
local access → Integer Overflow or Wraparound → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Local
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
High: exploitation depends on specific conditions
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness ?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-190: Integer Overflow or Wraparound. The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.
CVSS vector ?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L
Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVLocalAttack vector: The attacker needs local access to the vulnerable system.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.ALowAvailability impact: A successful attack can cause a limited loss.
Post-exploitation / living off the land
The issue can support a local privilege or sandbox boundary transition; normal system utilities may then be available in the gained context.
UnauthenticatedCWE-190
A
Official authority intelligence
Only matched European and national findings are included. Language selectors and unavailable sources are omitted.
ENISA EUVD · EUVD-2026-38181Official EUVD mapping
0 linked advisory records.
Official EUVD recordBSI · German · WID-SEC-2026-2025libexpat: Mehrere Schwachstellen ermöglichen nicht spezifizierten Angriff
Ein lokaler Angreifer kann mehrere Schwachstellen in libexpat ausnutzen, um einen nicht näher spezifizierten Angriff durchzuführen, darunter möglicherweise die Ausführung von beliebigem Code, die Manipulation von Daten, die Umgehung von Sicherheitsmaßnahmen, die Offenlegung vertraulicher Informationen oder die Herbeiführung eines Denial-of-Service-Zustands.
Operational remediation based on structured source evidence.
Status ?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
expat as a component of Red Hat Enterprise Linux 10; expat-devel as a component of Red Hat Enterprise Linux 10; expat.src as a component of Red Hat Enterprise Linux 10; firefox as a component of Red Hat Enterprise Linux 10; firefox.src as a component of Red Hat Enterprise Linux 10; thunderbird as a component of Red Hat Enterprise Linux 10; thunderbird.src as a component of Red Hat Enterprise Linux 10; compat-expat1 as a component of Red Hat Enterprise Linux 6; compat-expat1.src as a component of Red Hat Enterprise Linux 6; expat as a component of Red Hat Enterprise Linux 6; expat-devel as a component of Red Hat Enterprise Linux 6; expat.src as a component of Red Hat Enterprise Linux 6; expat as a component of Red Hat Enterprise Linux 7; expat-devel as a component of Red Hat Enterprise Linux 7; expat-static as a component of Red Hat Enterprise Linux 7; expat.src as a component of Red Hat Enterprise Linux 7; firefox as a component of Red Hat Enterprise Linux 7; firefox.src as a component of Red Hat Enterprise Linux 7; expat as a component of Red Hat Enterprise Linux 8; expat-devel as a component of Red Hat Enterprise Linux 8; expat.src as a component of Red Hat Enterprise Linux 8; firefox as a component of Red Hat Enterprise Linux 8; firefox.src as a component of Red Hat Enterprise Linux 8; mingw-expat.src as a component of Red Hat Enterprise Linux 8; mingw32-expat as a component of Red Hat Enterprise Linux 8; mingw64-expat as a component of Red Hat Enterprise Linux 8; thunderbird as a component of Red Hat Enterprise Linux 8; thunderbird.src as a component of Red Hat Enterprise Linux 8; xmlrpc-c as a component of Red Hat Enterprise Linux 8; xmlrpc-c-c++ as a component of Red Hat Enterprise Linux 8; and 14 more
Fixed
expat-main@aarch64 as a component of Red Hat Hardened Images; expat-main@src as a component of Red Hat Hardened Images; expat-main@x86_64 as a component of Red Hat Hardened Images
Action
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
Workaround
No verified workaround is recorded. Limit untrusted access and use least privilege until authoritative guidance is available.
04
Evidence and provenance
Published 21 Jun 2026 · Last source change 22 Jun 2026, 17:05 UTC · CWE-190 · Integer Overflow or Wraparound
CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source ?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-38181
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD enriched
Core structured fields are present and their contributing authorities are shown above.
Affected versionsThe structured affected or fixed version information changed.
Before
expat as a component of Red Hat Enterprise Linux 10; expat-devel as a component of Red Hat Enterprise Linux 10; expat.src as a component of Red Hat Enterprise Linux 10; firefox as a component of Red Hat Enterprise Linux 10; firefox.src as a component of Red Hat Enterprise Linux 10; thunderbird as a component of Red Hat Enterprise Linux 10; thunderbird.src as a component of Red Hat Enterprise Linux 10; compat-expat1 as a component of Red Hat Enterprise Linux 6; compat-expat1.src as a component of Red Hat Enterprise Linux 6; expat as a component of Red Hat Enterprise Linux 6; expat-devel as a component of Red Hat Enterprise Linux 6; expat.src as a component of Red Hat Enterprise Linux 6; expat as a component of Red Hat Enterprise Linux 7; expat-devel as a component of Red Hat Enterprise Linux 7; expat-static as a component of Red Hat Enterprise Linux 7; expat.src as a component of Red Hat Enterprise Linux 7; firefox as a component of Red Hat Enterprise Linux 7; firefox.src as a component of Red Hat Enterprise Linux 7; expat as a component of Red Hat Enterprise Linux 8; expat-devel as a component of Red Hat Enterprise Linux 8; expat.src as a component of Red Hat Enterprise Linux 8; firefox as a component of Red Hat Enterprise Linux 8; firefox.src as a component of Red Hat Enterprise Linux 8; mingw-expat.src as a component of Red Hat Enterprise Linux 8; mingw32-expat as a component of Red Hat Enterprise Linux 8; mingw64-expat as a component of Red Hat Enterprise Linux 8; thunderbird as a component of Red Hat Enterprise Linux 8; thunderbird.src as a component of Red Hat Enterprise Linux 8; xmlrpc-c as a component of Red Hat Enterprise Linux 8; xmlrpc-c-c++ as a component of Red Hat Enterprise Linux 8; and 13 more · Fixed: expat-main@aarch64 as a component of Red Hat Hardened Images; expat-main@src as a component of Red Hat Hardened Images; expat-main@x86_64 as a component of Red Hat Hardened Images
After
expat as a component of Red Hat Enterprise Linux 10; expat-devel as a component of Red Hat Enterprise Linux 10; expat.src as a component of Red Hat Enterprise Linux 10; firefox as a component of Red Hat Enterprise Linux 10; firefox.src as a component of Red Hat Enterprise Linux 10; thunderbird as a component of Red Hat Enterprise Linux 10; thunderbird.src as a component of Red Hat Enterprise Linux 10; compat-expat1 as a component of Red Hat Enterprise Linux 6; compat-expat1.src as a component of Red Hat Enterprise Linux 6; expat as a component of Red Hat Enterprise Linux 6; expat-devel as a component of Red Hat Enterprise Linux 6; expat.src as a component of Red Hat Enterprise Linux 6; expat as a component of Red Hat Enterprise Linux 7; expat-devel as a component of Red Hat Enterprise Linux 7; expat-static as a component of Red Hat Enterprise Linux 7; expat.src as a component of Red Hat Enterprise Linux 7; firefox as a component of Red Hat Enterprise Linux 7; firefox.src as a component of Red Hat Enterprise Linux 7; expat as a component of Red Hat Enterprise Linux 8; expat-devel as a component of Red Hat Enterprise Linux 8; expat.src as a component of Red Hat Enterprise Linux 8; firefox as a component of Red Hat Enterprise Linux 8; firefox.src as a component of Red Hat Enterprise Linux 8; mingw-expat.src as a component of Red Hat Enterprise Linux 8; mingw32-expat as a component of Red Hat Enterprise Linux 8; mingw64-expat as a component of Red Hat Enterprise Linux 8; thunderbird as a component of Red Hat Enterprise Linux 8; thunderbird.src as a component of Red Hat Enterprise Linux 8; xmlrpc-c as a component of Red Hat Enterprise Linux 8; xmlrpc-c-c++ as a component of Red Hat Enterprise Linux 8; and 14 more · Fixed: expat-main@aarch64 as a component of Red Hat Hardened Images; expat-main@src as a component of Red Hat Hardened Images; expat-main@x86_64 as a component of Red Hat Hardened Images
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
CVE-2026-56404: libexpat before 2.8.2 has an integer overflow in addBinding | BlackTree
