Stanza: RCE via pickle deserialization in the lemmatizer

Exploitation

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

CVSS

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

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

TL;DR Loading an attacker-supplied lemma `.pt` runs arbitrary code as the loading user. Since 1.14.0 the lemmatizer stores `pos_dict` as a gzip-compressed pickle in the checkpoint's `dicts` field (a `bytes` value). `torch.load(weights_only=True)` treats `bytes` as a primitive and passes it through unexamined, so its allowlist never sees the inner stream. `Trainer.load` then feeds those bytes to an unrestricted `pickle.loads`: the only bare `pickle.loads` in the tree. Result: `weights_only=True` gives no protection here, and model loading executes code. Confirmed end-to-end against stanza 1.14.0 / PyTorch 2.13.0 / CPython 3.13.7: a crafted checkpoint whose payload `reduce` returns `(os.system, (cmd,))` ran the command at load time (marker file showed `uid=501(...)`, `executed_by=...`). A downstream user is vulnerable whenever they build a pipeline that loads a caller-supplied lemmatizer checkpoint. i.e. `stanza.Pipeline(lang=..., processors="tokenize,pos,lemma",…

Published by the source

3 Nov 2026, 20:29 UTC

Last modified by the source

3 Nov 2026, 20:45 UTC

Source last checked

4 Nov 2026, 06:20 UTC

1. Revision 2 · amended · 4 Nov 2026

   Amended from osv record GHSA-gh9r-c94j-cmp5

2. Revision 1 · created · 3 Nov 2026

   Published from ghsa record GHSA-gh9r-c94j-cmp5

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# Patch Next advisory brief: CVE-2026-115878

Advisory: Stanza: RCE via pickle deserialization in the lemmatizer
IDs: CVE-2026-115878, GHSA-gh9r-c94j-cmp5
Record: https://patchnext.com/advisories/cve-2026-115878 (revision 2, source checked 4 Nov 2026, 06:20 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: stanza 1.15.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI stanza: affected >= 1.14.0, < 1.15.0; fixed in 1.15.0

## Suggested inspection (read-only)
- `python -m pip show stanza`: 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 stanza.
- 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://github.com/advisories/GHSA-gh9r-c94j-cmp5 (GitHub-reviewed advisory GHSA-gh9r-c94j-cmp5 lists affected ranges: PyPI stanza >=1.14.0 <=1.14.0)
- Verified: https://osv.dev/vulnerability/GHSA-gh9r-c94j-cmp5 (OSV record GHSA-gh9r-c94j-cmp5 lists affected ranges: PyPI stanza >=1.14.0 <1.15.0 (fixed))

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