Denial of Service Vulnerability in libexpat by Expat Software
CVE-2026-115506

8.7HIGH

Key Information:

Vendor

Libexpat

Status
Libexpat
Vendor
CVE Published:
22 October 2026

Badges

👾 Exploit Exists🟡 Public PoC

What is CVE-2026-115506?

libexpat versions through 2.9.0 present a denial of service vulnerability due to insufficient handling of entity expansion in XML documents. The 'billion laughs' attack exploits this flaw by using moderately sized XML files that contain a large Document Type Definition (DTD) with nested entities. This causes the parser to consume excessive CPU resources during parsing, resulting in significant performance degradation. For effective mitigation, it is crucial to upgrade to patched versions and implement additional safeguards against such attacks.

Affected Version(s)

libexpat 0 <= 2.9.0

Exploit Proof of Concept (PoC)

PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.

CVE-2026-115506 - Proof of Concept

References

https://github.com/libexpat/libexpat/pull/1433
patchissue-tracking
https://github.com/libexpat/libexpat/issues/1160
issue-tracking
https://github.com/hannob/lololol
exploit

CVSS V4

Score:
8.7
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • 🟡

    Public PoC available

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

Credit

Hanno Böck
Shani Yosef
.