GHSA-26c5-ppr8-f33p is a medium-severity (CVSS 5.4) Improper Authentication vulnerability in matrix-synapse. A fix is available for matrix-synapse — see the affected versions and patch details below.
Synapse has improper checks for deactivated users during login
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-26c5-ppr8-f33p.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-26c5-ppr8-f33p plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,166 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
matrix-synapseReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Impact
It may be possible for a deactivated user to login when using uncommon configurations.
This only applies if any of the following are true:
- JSON Web Tokens are enabled for login via the
jwt_config.enabledconfiguration setting - The local password database is enabled via the
password_config.enabledandpassword_config.localdb_enabledconfiguration settings and a user's password is updated via an admin API after a user is deactivated.
Note that the local password database is enabled by default, but it is uncommon to set a user's password after they've been deactivated.
Installations that are configured to only allow login via Single Sign-On (SSO) via CAS, SAML or OpenID Connect (OIDC); or via an external password provider (e.g. LDAP) are not affected.
Patches
- If using JSON Web Token logins: #15624
- For other users: #15634
Workarounds
If not using JSON Web Tokens, ensure that deactivated users do not have a password set. This list of users can be queried from PostgreSQL:
SELECT name FROM users WHERE password_hash IS NOT NULL AND deactivated = 1;
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | matrix-synapse | all versions | 1.85.0pip install --upgrade 'matrix-synapse==1.85.0' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for matrix-synapse, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update matrix-synapse to 1.85.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-26c5-ppr8-f33p is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-26c5-ppr8-f33p can be triaged on real exposure rather than presence alone.
Tailored to GHSA-26c5-ppr8-f33p. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-26c5-ppr8-f33p in your dependencies?
O3 Security finds GHSA-26c5-ppr8-f33p across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.