Description
Synapse is an open source Matrix homeserver implementation. Lack of validation for device keys in Synapse before 1.138.3 and in Synapse 1.139.0 allow an attacker registered on the victim homeserver to degrade federation functionality, unpredictably breaking outbound federation to other homeservers. The issue is patched in Synapse 1.138.3, 1.138.4, 1.139.1, and 1.139.2. Note that even though 1.138.3 and 1.139.1 fix the vulnerability, they inadvertently introduced an unrelated regression. For this reason, the maintainers of Synapse recommend skipping these releases and upgrading straight to 1.138.4 and 1.139.2.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| element-hq | synapse | < 1.138.3, = 1.139.0 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 24.04 LTS | matrix-synapse | No fix yet | — |
Show 3 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 22.04 LTS | matrix-synapse | No fix yet | — |
| Ubuntu Pro 20.04 LTS | matrix-synapse | No fix yet | — |
| Ubuntu Pro 18.04 LTS | matrix-synapse | No fix yet | — |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | matrix-synapse | 1.139.1-1.1 | openSUSE-SU-2025:15603-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | synapse | 1.139.2-r0 | — |
| Alpine v3.23 | synapse | 1.139.2-r0 | — |
| Alpine v3.22 | synapse | 1.139.2-r0 | — |
Affected packages
| Ecosystem | Package | Affected | Fixed | Record |
|---|---|---|---|---|
| PyPI | matrix-synapse | < 1.138.3 | 1.138.3 | GHSA-fh66-fcv5-jjfr |
| PyPI | matrix-synapse | >= 1.139.0rc2, < 1.139.1 | 1.139.1 | GHSA-fh66-fcv5-jjfr |
| PyPI | matrix-synapse | < 1.138.3 · >= 1.139.0rc2, < 1.139.1 | 1.138.3, 1.139.1 | PYSEC-2026-1612 |
Advisories 1
- openSUSE-SU-2025:15603-1 matrix-synapse-1.139.1-1.1 on GA media SUSE / openSUSE Security Updates · Mar 23, 2026
References
- https://github.com/element-hq/synapse/security/advisories/GHSA-fh66-fcv5-jjfr
- https://github.com/element-hq/synapse/pull/17097
- https://github.com/element-hq/synapse/commit/26aaaf9e48fff80cf67a20c691c75d670034b3c1
- https://github.com/element-hq/synapse/commit/7069636c2d6d1ef2022287addf3ed8b919ef2740
- https://github.com/element-hq/synapse/releases/tag/v1.138.3
- https://github.com/element-hq/synapse/releases/tag/v1.139.1