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CVE-2026-63097

MEDIUMCVSS 5.3/10EPSS 0.16%

Last modified

CVE-2026-63097 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. Dendrite through 0.13.8 contains an improper access control vulnerability in the syncapi /context endpoint (syncapi/routing/context.go) that allows authenticated local users to access post-leave room state events by exploiting a flawed membership check that evaluates only the RoomExists field while ignoring IsInRoom, HasBeenInRoom, and Membership fields. Attackers who have left a room can call the rooms context API endpoint for a previously permitted event and receive unfiltered current room state that the /messages and /sync endpoints correctly withhold.. EPSS estimates a 0.16% chance of exploitation in the next 30 days.

Description

Dendrite through 0.13.8 contains an improper access control vulnerability in the syncapi /context endpoint (syncapi/routing/context.go) that allows authenticated local users to access post-leave room state events by exploiting a flawed membership check that evaluates only the RoomExists field while ignoring IsInRoom, HasBeenInRoom, and Membership fields. Attackers who have left a room can call the rooms context API endpoint for a previously permitted event and receive unfiltered current room state that the /messages and /sync endpoints correctly withhold.

Metrics

CVSS 3.1
4.3/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

CVSS 4.0
5.3/10

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS Probability
0.16%

5.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

VendorProductVersions
matrix-orgdendrite<= 0.13.8

References

Timeline

Published
Last Modified
Status
Deferred

Frequently Asked Questions

What is CVE-2026-63097?
Dendrite through 0.13.8 contains an improper access control vulnerability in the syncapi /context endpoint (syncapi/routing/context.go) that allows authenticated local users to access post-leave room state events by exploiting a flawed membership check that evaluates only the RoomExists field while ignoring IsInRoom, HasBeenInRoom, and Membership fields. Attackers who have left a room can call the rooms context API endpoint for a previously permitted event and receive unfiltered current room state that the /messages and /sync endpoints correctly withhold.
How severe is CVE-2026-63097?
CVE-2026-63097 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 0.16% probability of exploitation in the next 30 days.
How do I fix CVE-2026-63097?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST