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Critical HTTP Request Smuggling Vulnerabilities in Cap'n Proto

Critical HTTP Request Smuggling Vulnerabilities in Cap'n Proto

First seen 20 Aug 2026, 11:54 UTC • •

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ThreatCluster AI
ThreatCluster •August 21, 2026 at 11:17 UTC
  • •Two critical vulnerabilities in Cap'n Proto could lead to HTTP request smuggling.
  • •Affected Ubuntu versions include 26.04, 24.04, 22.04, 20.04, and 18.04.
  • •Users are advised to apply updates to mitigate the risks associated with these vulnerabilities.

Two vulnerabilities (CVE-2026-32239, CVE-2026-32240) in Cap'n Proto were discovered by Chanho Kim and Jihyeok Han, allowing attackers to exploit improper handling of negative Content-Length values and large chunk sizes in HTTP messages. This could lead to HTTP request or response smuggling, potentially affecting systems using Cap'n Proto across multiple Ubuntu versions. The vulnerabilities were published on 2026-03-12. Users are advised to update their systems to the patched versions provided in the advisories. A standard system update will apply the necessary changes. The affected Ubuntu versions include 26.04, 24.04, 22.04, 20.04, and 18.04.

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Timeline

2026-03-12
CVE-2026-32239 published
CVE-2026-32239 was published, detailing a vulnerability in Cap'n Proto related to HTTP message handling.
Linuxsecurity
2026-03-12
CVE-2026-32240 published
CVE-2026-32240 was published, highlighting another vulnerability in Cap'n Proto affecting HTTP processing.
Ubuntu
2026-08-19
Vulnerabilities disclosed
Linuxsecurity and Ubuntu published advisories detailing the vulnerabilities in Cap'n Proto and their potential impact.
Linuxsecurity
2026-08-19
Patch availability announced
Both advisories confirmed that a standard system update will apply necessary patches for affected Ubuntu versions.
Ubuntu

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