Tornado: CurlAsyncHTTPClient leaks per-request credentials on handle reuse

Exploitation

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

CVSS

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

EPSS

• CVE-2026-91992: 0.24% estimated exploitation activity in the next 30 days; percentile 15.12 (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.

CurlAsyncHTTPClient leaks per-request credentials on handle reuse Summary CurlAsyncHTTPClient pools and reuses pycurl handles across requests but does not reset them between requests, and several per-request options are applied with no clearing branch. As a result, sensitive state set by one request persists onto a later request on the same client that does not set it. Two credential vectors are demonstrated below — a client TLS certificate (SSLCERT/SSLKEY) and proxy basic-auth credentials (PROXYUSERPWD) — both leaking to a different, unintended host. This affects all released versions through 6.5.6. Details In tornado/curlhttpclient.py, handles are created once and returned to a free list for reuse (processqueue pops the handle at line 200, finish re-appends it at line 245), and curlsetuprequest is never preceded by curl.reset(). The function clears some carried-over state on the reused handle — unsetopt(PROXYUSERPWD) in the no-proxy branch (line 394), unsetopt(USERPWD) when no auth…

Published by the source

15 Jun 2026, 20:37 UTC

Last modified by the source

16 Sep 2026, 03:56 UTC

Source last checked

26 Oct 2026, 13:45 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-pw6j-qg29-8w7f

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-pw6j-qg29-8w7f

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# Patch Next advisory brief: CVE-2026-91992

Advisory: Tornado: CurlAsyncHTTPClient leaks per-request credentials on handle reuse
IDs: CVE-2026-91992, GHSA-pw6j-qg29-8w7f
Record: https://patchnext.com/advisories/cve-2026-91992 (revision 2, source checked 26 Oct 2026, 13:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: tornado 6.5.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI tornado: affected <= 6.5.6; fixed in 6.5.7

## 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://osv.dev/vulnerability/GHSA-pw6j-qg29-8w7f (OSV record GHSA-pw6j-qg29-8w7f lists affected ranges: PyPI tornado >=0 <6.5.7 (fixed))
- Verified: https://github.com/advisories/GHSA-pw6j-qg29-8w7f (GitHub-reviewed advisory GHSA-pw6j-qg29-8w7f lists affected ranges: PyPI tornado >=0 <=6.5.6)

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