Description
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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| capnproto | capnproto | < 1.4.0 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | capnproto | 1.4.0-2 | — |
| Debian 13 | capnproto | No fix yet | — |
| Debian 12 | capnproto | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | capnproto | 1.4.0-3build1 | — |
| Ubuntu 25.10 | capnproto | No fix yet | — |
Show 5 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 26.04 LTS | capnproto | 1.1.0-2.1ubuntu0.1~esm1 | USN-8650-1 |
| Ubuntu Pro 24.04 LTS | capnproto | 1.0.1-4ubuntu0.1~esm1 | USN-8650-1 |
| Ubuntu Pro 22.04 LTS | capnproto | 0.8.0-2ubuntu2+esm1 | USN-8650-1 |
| Ubuntu Pro 20.04 LTS | capnproto | 0.7.0-6ubuntu0.1~esm1 | USN-8650-1 |
| Ubuntu Pro 18.04 LTS | capnproto | 0.6.1-1ubuntu1+esm1 | USN-8650-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Leap 16.0 | capnproto | 1.4.0-160000.1.1 | openSUSE-SU-2026:21062-1 |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | capnproto | No fix yet | — |
Advisories 2
- USN-8650-1 capnproto vulnerabilities Ubuntu Security Notices (USN) · Aug 20, 2026
- openSUSE-SU-2026:21062-1 Security update for capnproto SUSE / openSUSE Security Updates · Jun 30, 2026
References
- https://github.com/capnproto/capnproto/security/advisories/GHSA-vpcq-mx5v-32wm
- https://github.com/capnproto/capnproto/commit/2744b3c012b4aa3c31cefb61ec656829fa5c0e36
- https://github.com/capnproto/capnproto/commit/e929f0ba7901a6b8f4b5ba9a4db00af43288cbb0
- https://capnproto.org/capnproto-c++-1.4.0.tar.gz
- https://capnproto.org/capnproto-c++-win32-1.4.0.zip