Machine-written summary
Summary written by Claude Haiku from the source advisory. Not reviewed by a person.
Versions of pyzipper before 0.4.0 write encrypted ZIP entries in the AE-1 format by default, which stores the plaintext CRC32 checksum unencrypted in the archive header. An attacker who has the archive can use that checksum to guess the contents of small or low-entropy files, though the AES encryption itself is not broken. Upgrade to pyzipper 0.4.0, which uses AE-2 and omits CRC32 values by default; rewriting existing archives to remove the checksums requires recreating the whole archive.
Not analysed yet
We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.
Severity and exploitation
| Score | Rating | CVSS | Vector | Source |
|---|---|---|---|---|
| 6.2 | Medium | 3.1 | CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N | CNA (GitHub_M) |
- CISA KEV Not listed.
- EPSS 0.0012, the 1st percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.
Timeline
- 31 Oct 2026, 15:01 UTC First seen by agentprime
- 31 Oct 2026, 15:01 UTC Confirmed by OSV