What’s Vulnerable › Vulnerabilities

CVE-2026-115506: libexpat through 2.9.0 Denial of Service via Billion Laughs Detection Delay

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-22 · updated 2026-10-23
• Weakness: CWE-776

Description

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.

Affected products

• libexpat: through 2.9.0

References

• https://github.com/hannob/lololol
• https://github.com/libexpat/libexpat
• https://github.com/libexpat/libexpat/issues/1160
• https://github.com/libexpat/libexpat/pull/1433
• https://www.vulncheck.com/advisories/libexpat-through-2.9.0-denial-of-service-via-billion-laughs-detection-delay

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