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19Track

Red Hat: Flaw was found in the ChunkReader component of the Undertow web server

Red Hat · CVE-2026-91920 EUVD-2026-113473 GHSA-3F65-G3HR-C59R
0 news outlets1 CERTs and agencies0 research labs

Assessment: Track

SSVC decision points: exploitation none, automatable yes, technical impact partial, deployment low.

What is it?

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.

Evidence

Official warnings1National CERTs, government cyber security agencies and the vendor’s own advisories

Exploitation

  • Exploit code published (not verified by us)
  • Exploited in the wild (confirmed by a source)
  • Listed as known exploited (CISA KEV)
CVSS
6.5
EPSS
–
First seen
1 h ago
Status
confirmed

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