Billion laughs detection delay in libexpat enables denial of service
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- None
- Impact type
- —
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- No fix listed
Attack profile from CVSS 4.0 · CNA. Fix status from CNA and Red Hat.
Summary
libexpat through 2.9.0 has a denial of service flaw in accountingDiffTolerated() in xmlparse.c, where billion laughs protection detects entity amplification too late (CWE-776). A remote attacker without privileges or user interaction can supply a moderately sized XML document with a large DTD and nested entity expansions, consuming tens of seconds of CPU per parse. A public exploit is linked in the references.
Written with Claude Haiku 5.5 from the sources below · 2026-11-06
Description from the CNA
libexpat through 2.9.0 contains a denial of service vulnerability because billion laughs protection in accountingDiffTolerated() in xmlparse.c detects entity amplification too late. Attackers can supply a moderately sized XML document with a large DTD and nested entity expansions to consume tens of seconds of CPU per parse.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| libexpat project | libexpat | up to 2.9.0 | — | No fix listed | CNA |
- libexpat Vendorlibexpat project Affected up to 2.9.0 Fixed in — No fix listed CNA
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:libexpat_project:libexpat:*:*:*:*:*:*:*:* | up to 2.9.0 | Vulnerable | libexpat project |
- cpe:2.3:a:libexpat_project:libexpat:*:*:*:*:*:*:*:* Versions up to 2.9.0 Vulnerable ·libexpat project
Remediation
No fixed version is listed for libexpat. Red Hat lists Red Hat Enterprise Linux 7, 8, 9 and 10, Red Hat Hardened Images, and Red Hat OpenShift Container Platform 4 and 5 as affected without a fix and with no plan available.
Written with Claude Haiku 5.5 from the sources below · 2026-11-06
Vendor assessments
Red Hat
Red Hat rating: Important. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 10 | Affected | No fix yet |
| Red Hat Enterprise Linux 7 | Affected | No fix yet |
| Red Hat Enterprise Linux 8 | Affected | No fix yet |
| Red Hat Enterprise Linux 9 | Affected | No fix yet |
| Red Hat Hardened Images | Affected | No fix yet |
| Red Hat OpenShift Container Platform 4 | Affected | No fix yet |
| Red Hat OpenShift Container Platform 5 | Affected | No fix yet |
Not affected: 3 products
- Red Hat Enterprise Linux 6
- Red Hat Enterprise Linux 7
- Red Hat Enterprise Linux 8
Timeline
- 2026-10-22 Threatist record created from CVE-2026-115506
- 2026-10-22 Alias added: GHSA-j83x-34mv-v962
- 2026-10-23 Priority changed: MEDIUM → LOW
- 2026-10-24 CISA SSVC decision points changed
- 2026-10-24 Priority changed: LOW → HIGH
- 2026-11-06 Affected versions changed · Red Hat
- 2026-11-06 CVSS score added · Red Hat
References
More libexpat project Libexpat vulnerabilities
- TI-2022-09008 In Expat (aka libexpat) before 2.4.5, there is an integer overflow in storeRawNames. CVSS 3.1CRITICAL 9.8
- TI-2022-08947 xmlparse.c in Expat (aka libexpat) before 2.4.5 allows attackers to insert… CVSS 3.1CRITICAL 9.8
- TI-2021-20962 In Expat (aka libexpat) before 2.4.3, a left shift by 29 (or more) places in the… CVSS 3.1HIGH 8.8
- TI-2021-21076 In doProlog in xmlparse.c in Expat (aka libexpat) before 2.4.3, an integer overflow exists for m_groupSize. CVSS 3.1HIGH 8.1
- TI-2016-00645 Expat allows context-dependent attackers to cause a denial of service (crash) or possibly… CVSS 3.1CRITICAL 9.8
- TI-2024-34028 An issue was discovered in libexpat before 2.6.4. CVSS 3.1MEDIUM 5.9
Sources
- CVE-2026-115506 · CVE Program
- CVE-2026-115506 · NVD
- FIRST EPSS
- GHSA-j83x-34mv-v962 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-115506 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences