Vulnerability in Capnproto
CVE-2026-32240
Cap'n Proto is a data interchange format and capability-based RPC system. Prior to 1.4.0, when using Transfer-Encoding: chunked, if a chunk's size parsed to a value of 2^64 or larger, it would be truncated to a 64-bit integer. In theory, this bug could enable HTTP request/response smuggling. This vulnerability is fixed in 1.4.0.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.004 (26.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 27th percentile — 26.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.004 · change: +0.001
Affected products
- Capnproto — versions < 1.4.0
Weakness classification (CWE)
References
- github.com/capnproto/capnproto/security/advisories/GHSA-vpcq-mx5v-32wm (Vendor Advisory)
- github.com/capnproto/capnproto/commit/2744b3c012b4aa3c31cefb61ec656829fa5c0e36 (Patch)
- github.com/capnproto/capnproto/commit/e929f0ba7901a6b8f4b5ba9a4db00af43288cbb0 (Patch)
- capnproto.org/capnproto-c++-1.4.0.tar.gz (Product)
- capnproto.org/capnproto-c++-win32-1.4.0.zip (Product)
Frequently asked questions
- What is CVE-2026-32240?
- CVE-2026-32240 is a medium-severity vulnerability in Capnproto, classified under CWE-197. CVSS score: 6.5/10. Published 2026-03-12.
- How severe is CVE-2026-32240?
- Medium severity. CVSS v3 base score is 6.5 out of 10.