py7zr: Arbitrary File Write Vulnerability

Exploitation

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

CVSS

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

EPSS

• CVE-2026-23879: 0.50% estimated exploitation activity in the next 30 days; percentile 42.71 (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.

Summary There exists an arbitrary file write vulnerability in py7zr (1.1.0, latest), which allows symbolic links to be recreated outside the destination directory via crafted malicious symbolic link chains. When using extractall to extract an archive, the library restores these symbolic links, linking them to arbitrary directories on the host file system. Subsequent extraction of regular files through these symbolic links can result in arbitrary file writes. This vulnerability may lead to remote code execution, privilege escalation, data corruption, or denial of service. Details The root cause of this vulnerability is that py7zr fails to properly restrict the targets of symbolic links within an archive. During extraction, the program only checks the link arcname within the destination directory, but ignores the combined symlink path resolution. Attackers can exploit this vulnerability by constructing malicious archives, thereby bypassing the directory boundary restrictions…

Published by the source

19 Jun 2026, 19:21 UTC

Last modified by the source

21 Jul 2026, 13:30 UTC

Source last checked

26 Oct 2026, 13:49 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-q6rc-2cgv-63h7

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-q6rc-2cgv-63h7

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# Patch Next advisory brief: CVE-2026-23879

Advisory: py7zr: Arbitrary File Write Vulnerability
IDs: CVE-2026-23879, GHSA-q6rc-2cgv-63h7
Record: https://patchnext.com/advisories/cve-2026-23879 (revision 2, source checked 26 Oct 2026, 13:49 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.0)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: py7zr 1.1.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI py7zr: affected <= 1.1.2; fixed in 1.1.3

## Suggested inspection (read-only)
- `python -m pip show py7zr`: 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 py7zr.
- 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-q6rc-2cgv-63h7 (OSV record GHSA-q6rc-2cgv-63h7 lists affected ranges: PyPI py7zr >=0 <1.1.3 (fixed))
- Verified: https://github.com/advisories/GHSA-q6rc-2cgv-63h7 (GitHub-reviewed advisory GHSA-q6rc-2cgv-63h7 lists affected ranges: PyPI py7zr >=0 <=1.1.2)

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