Tornado: StaticFileHandler follows symlinks outside static root (path traversal)

Exploitation

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

CVSS 4.0

8.2 · CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-103263: 0.52% estimated exploitation activity in the next 30 days; percentile 44.38 (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 StaticFileHandler allows an unauthenticated attacker to read arbitrary files from the server's filesystem by requesting a path that resolves to a symbolic link placed inside the static root directory. Any application that serves user-uploadable content, or whose static directory is populated by a build/deploy pipeline that creates symlinks (e.g. npm link, webpack, Docker volume mounts, CDN sync tools), is affected. An attacker who can trigger the creation of a symlink pointing outside the static root—or exploit one that already exists—can retrieve sensitive files such as /etc/passwd, private keys, configuration files, or application secrets. Details The vulnerability is in tornado.web.StaticFileHandler, specifically in the interaction between two methods in tornado/web.py: - getabsolutepath uses os.path.abspath() to resolve the requested path: - validateabsolutepath uses the same os.path.abspath() on the root, then performs a string prefix check: os.path.abspath() normalises…

Published by the source

30 Sep 2026, 23:48 UTC

Last modified by the source

2 Oct 2026, 03:56 UTC

Source last checked

26 Oct 2026, 13:54 UTC

1. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-c2m8-h5v5-343r

2. Revision 3 · amended · 24 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-c2m8-h5v5-343r

4. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-c2m8-h5v5-343r

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# Patch Next advisory brief: CVE-2026-103263

Advisory: Tornado: StaticFileHandler follows symlinks outside static root (path traversal)
IDs: CVE-2026-103263, GHSA-c2m8-h5v5-343r
Record: https://patchnext.com/advisories/ghsa-c2m8-h5v5-343r (revision 4, source checked 26 Oct 2026, 13:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: tornado 6.5.9. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI tornado: affected <= 6.5.8; fixed in 6.5.9

## Suggested inspection (read-only)
- `python -m pip show tornado`: 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 tornado.
- 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-c2m8-h5v5-343r (GitHub-reviewed advisory GHSA-c2m8-h5v5-343r lists affected ranges: PyPI tornado >=0 <=6.5.8)
- Verified: https://osv.dev/vulnerability/GHSA-c2m8-h5v5-343r (OSV record GHSA-c2m8-h5v5-343r lists affected ranges: PyPI tornado >=0 <6.5.9 (fixed))

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