pyzipper has an encryption bypass for small files encrypted using it

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.2 · CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS

• CVE-2026-44722: 0.12% estimated exploitation activity in the next 30 days; percentile 1.64 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact A Python operator precedence bug in pyzipper/zipfileaes.py caused the AE-2 format to never be automatically selected during encryption, regardless of file size or compression type. As a result, all encrypted entries are written in AE-1 format unless AE-2 is explicitly forced by the caller. AE-1 stores the plaintext CRC32 checksum unencrypted in the ZIP header. During investigation of this issue, it was also found that when writing to an unseekable zip archive, the CRC32 value was always written to the datadescripter section. The AES encryption itself is not broken. An attacker who possesses the archive can read the CRC32 from the header without decrypting anything, then brute-force candidate plaintexts by computing CRC32(candidate) and comparing against the stored value. In practice, this attack is feasible today only against small or low-entropy files, as CRC32 exhaustion across a large plaintext space is computationally prohibitive on current hardware. Files with…

Published by the source

14 May 2026, 16:17 UTC

Last modified by the source

13 Jul 2026, 16:43 UTC

Source last checked

26 Oct 2026, 13:41 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-crqm-m339-7m2p

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-crqm-m339-7m2p

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# Patch Next advisory brief: CVE-2026-44722

Advisory: pyzipper has an encryption bypass for small files encrypted using it
IDs: CVE-2026-44722, GHSA-crqm-m339-7m2p
Record: https://patchnext.com/advisories/cve-2026-44722 (revision 2, source checked 26 Oct 2026, 13:41 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pyzipper 0.4.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI pyzipper: affected < 0.4.0; fixed in 0.4.0

## Suggested inspection (read-only)
- `python -m pip show pyzipper`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on pyzipper.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-crqm-m339-7m2p (OSV record GHSA-crqm-m339-7m2p lists affected ranges: PyPI pyzipper >=0 <0.4.0 (fixed))
- Verified: https://github.com/advisories/GHSA-crqm-m339-7m2p (GitHub-reviewed advisory GHSA-crqm-m339-7m2p lists affected ranges: PyPI pyzipper >=0 <0.4.0)

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