Chainlit contains a session hijacking vulnerability

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2026-56104: 0.42% estimated exploitation activity in the next 30 days; percentile 36.02 (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.

Chainlit before 2.10.1 contains a session hijacking vulnerability that allows unauthenticated attackers to restore and inherit authenticated user sessions by presenting a valid sessionId during WebSocket session restoration without ownership verification. Attackers can exploit the restoreexistingsession path to assume a victim's permissions and roles, enabling unauthorized invocation of tools and access to data restricted to the authenticated victim.

Published by the source

22 Jun 2026, 18:34 UTC

Last modified by the source

1 Oct 2026, 17:56 UTC

Source last checked

26 Oct 2026, 13:54 UTC

1. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-c39v-8hrw-h448

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-c39v-8hrw-h448

4. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-c39v-8hrw-h448

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# Patch Next advisory brief: CVE-2026-56104

Advisory: Chainlit contains a session hijacking vulnerability
IDs: CVE-2026-56104, GHSA-c39v-8hrw-h448
Record: https://patchnext.com/advisories/cve-2026-56104 (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: Critical (CVSS 9.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: chainlit 2.10.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI chainlit: affected < 2.10.1; fixed in 2.10.1

## Suggested inspection (read-only)
- `python -m pip show chainlit`: 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 chainlit.
- 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-c39v-8hrw-h448 (GitHub-reviewed advisory GHSA-c39v-8hrw-h448 lists affected ranges: PyPI chainlit >=0 <2.10.1)
- Verified: https://osv.dev/vulnerability/GHSA-c39v-8hrw-h448 (OSV record GHSA-c39v-8hrw-h448 lists affected ranges: PyPI chainlit >=0 <2.10.1 (fixed))

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