Description
HKDF in cryptography before 1.5.2 returns an empty byte-string if used with a length less than algorithm.digest_size.
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 | python-cryptography | 1.5.3-1 | — |
| Debian 13 | python-cryptography | 1.5.3-1 | — |
| Debian 12 | python-cryptography | 1.5.3-1 | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 16.04 LTS | python-cryptography | 1.2.3-1ubuntu0.1 | USN-3138-1 |
Affected packages
| Ecosystem | Package | Affected | Fixed | Record |
|---|---|---|---|---|
| PyPI | cryptography | < 1.5.3 | 1.5.3 | GHSA-q3cj-2r34-2cwc |
Advisories 1
- USN-3138-1 python-cryptography vulnerability Ubuntu Security Notices (USN) · Feb 10, 2026
References
- FEDORA-2016-2d90e27e50 vendor-advisory
- USN-3138-1 vendor-advisory
- https://github.com/pyca/cryptography/commit/b924696b2e8731f39696584d12cceeb3aeb2d874
- FEDORA-2016-d3a2b640ce vendor-advisory
- 94216 vdb-entry
- [oss-security] 20161109 Re: CVE Request: Cryptography 1.5.3: HKDF might return an empty byte-string mailing-list
- https://cryptography.io/en/latest/changelog
- FEDORA-2016-e77c8c1f3b vendor-advisory
- https://github.com/pyca/cryptography/issues/3211