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CVE-2026-91920: Undertow: undertow: chunkreader message length permits chunk-size overflow

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-30 · updated 2026-10-30
• Weakness: CWE-444

Description

A flaw was found in the ChunkReader component of the Undertow web server, which is used to handle chunked transfer encoding in HTTP requests. The issue occurs because a security check for the chunk size is performed before the value is shifted, allowing a specifically crafted 15-digit chunk size to bypass the limit and overflow into internal state flags. This can cause the server to terminate a request body prematurely and interpret the remaining data as a separate, smuggled request.

Affected products

• Red Hat build of Apache Camel for Spring Boot 4: all versions
• Red Hat Fuse 7: all versions
• Red Hat JBoss Enterprise Application Platform 7: all versions
• Red Hat JBoss Enterprise Application Platform 8: all versions
• Red Hat Single Sign-On 7: all versions

References

• https://access.redhat.com/security/cve/CVE-2026-91920
• https://bugzilla.redhat.com/show_bug.cgi?id=2528758

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