Security Digest · Vulnerability record
CVE-2026-56104: Chainlit contains a session hijacking vulnerability
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.
CVSS 8.8 High EPSS 0.4% · p35
Should you act?
Normal patch cycle
No exploitation signal; fix it in your next routine update if you are affected. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.4%, percentile 35: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 35% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Needs an account (low (any account)). Exposure depends on who can log in.
- Only applies if your dependency tree includes
chainlit(PyPI) < 2.10.1, fixed in 2.10.1. Check your lockfile, including transitive dependencies.
What it is
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.
From the GitHub advisory
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.
Weakness type: CWE-862.
Product: chainlit (PyPI) · Assigned by: VulnCheck · Published: 2026-06-22
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| PyPI | chainlit | < 2.10.1 | 2.10.1 |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| Chainlit | chainlit | < 2.10.1 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| VulnCheck | 4.0 | 8.8 High | CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N |
| VulnCheck | 3.1 | 8.2 High | CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N |
| GitHub | 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 |
- Attack vector: network (remotely reachable)
- Attack complexity: high (needs special conditions)
- Attack requirements: none
- Privileges required: low (any account)
- User interaction: none
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none, automatable no, technical impact total.
- FIRST EPSS (model of 2026-10-21): 0.42% probability of exploitation activity in the next 30 days; percentile 35.
Timeline
- — CVE record published by VulnCheck
- — GitHub-reviewed advisory GHSA-c39v-8hrw-h448 published (critical)
- — CVE record last updated
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vendor and project advisories, patches
- Release Notes github.com
- Patch Commit github.com
Vulnerability records
- GitHub Advisory GHSA-c39v-8hrw-h448 github.com
- CVE.org record CVE-2026-56104 cve.org
- NVD entry CVE-2026-56104 nvd.nist.gov
Other references from the CVE record and advisory
- Pull Request github.com
- vulncheck.com vulncheck.com