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Medium

Synapse's invalid device keys degrade federation functionality

  • Disclosed: 08.10.2025
  • Updated: 11.10.2026 13:18

Impact

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.

Patches

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, it is recommend to skip these releases and upgrading straight to 1.138.4 and 1.139.2.

Workarounds

The vulnerability can only be exploited by users registered on the victim homeserver.

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
Python (PyPI) matrix-synapse < 1.138.3, >= 1.139.0rc2, < 1.139.1 1.138.3, 1.139.1

References

CVSS score -
CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N
Weakness (CWE)
CWE-1287
Platform
Python (PyPI)
Package
matrix-synapse
Disclosed
08.10.2025
Updated
11.10.2026 13:18

Sources and licenses

OSV / GitHub Advisory Database - PYSEC-2026-1612 - PyPA Advisory Database; CC BY 4.0

OSV / GitHub Advisory Database - GHSA-fh66-fcv5-jjfr - CC BY 4.0

Vulnerability history: matrix-synapse

All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (45) in the archive
Total entries
45
First → latest
03.2019 05.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • High 21
  • Medium 21
  • Low 3

Disclosures per year

Severity:
  1. Synapse CPU starvation (Denial of Service)
    High · 5.5 CVE-2026-45078 < 1.152.1 1.152.1
  2. Synapse's invalid device keys degrade federation functionality this entry
    Medium CVE-2025-61672 < 1.138.3, >= 1.139.0rc2, < 1.139.1 1.138.3, 1.139.1
  3. Synapse vulnerable to federation denial of service via malformed events
    High · 7.1 CVE-2025-30355 < 1.127.1 1.127.1
  4. Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders
    High CVE-2024-53863 < 1.120.1 1.120.1
  5. Synapse allows a a malformed invite to break the invitee's `/sync`
    High CVE-2024-52815 < 1.120.1 1.120.1
  6. Synapse allows unsupported content types to lead to memory exhaustion
    High CVE-2024-52805 < 1.120.1 1.120.1
  7. Synapse denial of service through media disk space consumption
    High · 7.5 CVE-2024-37302 < 1.106 1.106
  8. Synapse Denial of service due to incorrect application of event authorization rules during state resolution
    High · 6.5 CVE-2022-39374 >= 1.62.0, < 1.68.0rc1 1.68.0rc1
  9. Synapse does not apply enough checks to servers requesting auth events of events in a room
    High · 5.0 CVE-2022-39335 < 1.69.0 1.69.0
  10. Denial of service due to incorrect application of event authorization rules
    High · 7.5 CVE-2022-31152 < 1.62.0rc1 1.62.0rc1
  11. URL previews of unusual or maliciously-crafted pages can crash Synapse media repositories or Synapse monoliths
    High · 6.5 CVE-2022-31052 < 1.61.1 1.61.1
  12. Matrix Synapse DoS
    High · 7.5 CVE-2018-10657 < 0.28.1 0.28.1
  13. Matrix Synapse Improper Signature Validation
    High · 8.8 CVE-2018-16515 >= 0.33.3, < 0.33.3.1, < 0.33.2.1 0.33.3.1, 0.33.2.1
  14. Matrix Synapse Authorization Error
    High · 7.5 CVE-2018-12423 < 0.31.2 0.31.2
  15. Matrix Synapse Security Filtering Flaw
    High · 7.5 CVE-2018-12291 < 0.31.1 0.31.1
  16. Path traversal in Matrix Synapse
    High · 7.5 CVE-2021-41281 < 1.47.1 1.47.1
  17. Open redirect via transitional IPv6 addresses on dual-stack networks
    High · 6.3 CVE-2021-21392 < 1.28.0rc1 1.28.0rc1
  18. Denial of service attack via incorrect parameters in Matrix Synapse
    High · 6.5 CVE-2020-26257 < 1.23.1 1.23.1
  19. Denial of service attack due to invalid JSON
    High · 7.5 CVE-2020-26890 < 1.20.0 1.20.0
  20. Improper Verification of Cryptographic Signature in matrix-synapse
    High · 8.6 CVE-2019-18835 < 1.5.0 1.5.0
Show more (2) Showing 20 of 22

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