USN-8650-1: Cap'n Proto vulnerabilities
Chanho Kim and Jihyeok Han discovered that Cap'n Proto incorrectly handled negative Content-Length values or excessively large chunk sizes when processing HTTP messages. An attacker could possibly use these issues to cause HTTP messages to be interpreted inconsistently, resulting in HTTP request or response smuggling. (CVE-2026-32239, CVE-2026-32240)
CSIRTS triage
- What
- Incorrect handling of negative Content-Length values and excessively large chunk sizes in HTTP message processing enables HTTP request or response smuggling.
- Who is affected
- Systems using Cap'n Proto for HTTP message processing are affected.
- Urgency
- Moderate urgency; HTTP smuggling can lead to request confusion and cache poisoning but requires specific conditions.
- Action
- Update Cap'n Proto to a patched version addressing CVE-2026-32239 and CVE-2026-32240.
AI-assisted analysis generated from the source advisory — verify against the original.
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Details
Original advisory: https://ubuntu.com/security/notices/USN-8650-1
Exploitation outlook
EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.
- Low exploitation riskCVE-2026-322390.21% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 11% of all EPSS-scored CVEs.
- Low exploitation riskCVE-2026-322400.21% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 11% of all EPSS-scored CVEs.
Referenced CVEs
| CVE | CSIRTS overview | External |
|---|---|---|
| CVE-2026-32239 | coverage & exploitation status | NVD · CVE.org |
| CVE-2026-32240 | coverage & exploitation status | NVD · CVE.org |
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