CVE-2020-26257

MEDIUMNVD 6.56.5
EchelonGraph scoreLOW confidence

This medium-severity CVE scores 6.5 under NVD CVSS v3. EPSS exploit-prediction score not yet available (the EPSS model rescores nightly; freshly-published CVEs typically appear within 48 hours). GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: nvd
6.5
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 2%CVSS: 6.5Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

Matrix is an ecosystem for open federated Instant Messaging and VoIP. Synapse is a reference "homeserver" implementation of Matrix. A malicious or poorly-implemented homeserver can inject malformed events into a room by specifying a different room id in the path of a /send_join, /send_leave, /invite or /exchange_third_party_invite request. This can lead to a denial of service in which future events will not be correctly sent to other servers over federation. This affects any server which accepts federation requests from untrusted servers. The Matrix Synapse reference implementation before version 1.23.1 the implementation is vulnerable to this injection attack. Issue is fixed in version 1.23.1. As a workaround homeserver administrators could limit access to the federation API to trusted servers (for example via federation_domain_whitelist).

CVSS v3
6.5
EG Score
6.5(low)
EPSS
81.8%
KEV
Not listed

Published

December 9, 2020

Last Modified

November 21, 2024

References (12)

Affected Packages

(1 across 1 ecosystem)
PyPI(1)
PackageVulnerable rangeFixed inDependents
matrix-synapse0.33.5 ... 1.9.1 (138 versions)1.23.1—

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 9× in last 7d / 39× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-11 08:25 UTCEPSS rescore
  2. 2026-07-11 08:25 UTCEPSS rescore
  3. 2026-07-09 19:07 UTCEPSS rescore
  4. 2026-07-08 15:12 UTCEPSS rescore
  5. 2026-07-07 13:43 UTCEPSS rescore
  6. 2026-07-06 16:25 UTCEPSS rescore
  7. 2026-07-06 16:25 UTCEPSS rescore
  8. 2026-07-06 02:21 UTCEPSS rescore
  9. 2026-07-06 02:21 UTCEPSS rescore
  10. 2026-07-04 06:29 UTCEPSS rescore
  11. 2026-07-04 06:29 UTCEPSS rescore
  12. 2026-06-30 23:20 UTCEPSS rescore
  13. 2026-06-30 23:20 UTCEPSS rescore
  14. 2026-06-29 14:04 UTCEPSS rescore
  15. 2026-06-28 04:54 UTCEPSS rescore
  16. 2026-06-28 04:54 UTCEPSS rescore
  17. 2026-06-27 03:06 UTCEPSS rescore
  18. 2026-06-27 03:06 UTCEPSS rescore
  19. 2026-06-25 13:48 UTCEPSS rescore
  20. 2026-06-24 14:03 UTCEPSS rescore
  21. 2026-06-24 14:03 UTCEPSS rescore
  22. 2026-06-24 07:59 UTCOSV refresh
  23. 2026-06-23 21:31 UTCEPSS rescore
  24. 2026-06-23 21:31 UTCEPSS rescore
  25. 2026-06-22 14:23 UTCEPSS rescore
Show 48 more
  1. 2026-06-22 14:23 UTCEPSS rescore
  2. 2026-06-21 14:54 UTCEPSS rescore
  3. 2026-06-21 14:54 UTCEPSS rescore
  4. 2026-06-21 01:57 UTCEPSS rescore
  5. 2026-06-19 19:24 UTCEPSS rescore
  6. 2026-06-19 19:23 UTCEPSS rescore
  7. 2026-06-18 17:50 UTCEPSS rescore
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  9. 2026-06-17 17:50 UTCEPSS rescore
  10. 2026-06-16 17:50 UTCEPSS rescore
  11. 2026-06-15 17:46 UTCEPSS rescore
  12. 2026-06-14 23:15 UTCEPSS rescore
  13. 2026-06-13 22:58 UTCEPSS rescore
  14. 2026-06-12 23:10 UTCEPSS rescore
  15. 2026-06-11 13:58 UTCEPSS rescore
  16. 2026-06-10 22:16 UTCEPSS rescore
  17. 2026-06-10 13:20 UTCEPSS rescore
  18. 2026-06-08 14:15 UTCEPSS rescore
  19. 2026-06-07 15:23 UTCEPSS rescore
  20. 2026-06-07 15:23 UTCEPSS rescore
  21. 2026-06-07 15:23 UTCEPSS rescore
  22. 2026-06-07 11:59 UTCOSV refresh
  23. 2026-06-06 13:46 UTCEPSS rescore
  24. 2026-06-06 13:45 UTCEPSS rescore
  25. 2026-06-05 22:45 UTCEPSS rescore
  26. 2026-06-05 22:45 UTCEPSS rescore
  27. 2026-06-05 06:08 UTCEPSS rescore
  28. 2026-06-05 06:08 UTCEPSS rescore
  29. 2026-06-04 13:10 UTCEPSS rescore
  30. 2026-06-04 13:10 UTCEPSS rescore
  31. 2026-06-02 20:11 UTCEPSS rescore
  32. 2026-06-02 20:11 UTCEPSS rescore
  33. 2026-06-01 13:50 UTCEPSS rescore
  34. 2026-06-01 13:50 UTCEPSS rescore
  35. 2026-05-31 22:29 UTCEPSS rescore
  36. 2026-05-31 22:29 UTCEPSS rescore
  37. 2026-05-31 00:15 UTCEPSS rescore
  38. 2026-05-31 00:15 UTCEPSS rescore
  39. 2026-05-29 13:42 UTCEPSS rescore
  40. 2026-05-28 13:43 UTCEPSS rescore
  41. 2026-05-28 13:43 UTCEPSS rescore
  42. 2026-05-27 13:39 UTCEPSS rescore
  43. 2026-05-26 13:42 UTCEPSS rescore
  44. 2026-05-26 13:42 UTCEPSS rescore
  45. 2026-05-26 07:17 UTCEPSS rescore
  46. 2026-05-26 07:17 UTCEPSS rescore
  47. 2026-05-24 16:48 UTCEPSS rescore
  48. 2026-05-23 04:29 UTCEG score recompute

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2020-26257?
CVE-2020-26257 is a medium vulnerability published on December 9, 2020. Matrix is an ecosystem for open federated Instant Messaging and VoIP. Synapse is a reference "homeserver" implementation of Matrix. A malicious or poorly-implemented homeserver can inject malformed events into a room by specifying a different room id in the path of a /sendjoin, /sendleave, /invite…
When was CVE-2020-26257 disclosed?
CVE-2020-26257 was first published in the National Vulnerability Database on December 9, 2020, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2020-26257 actively exploited?
CVE-2020-26257 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 81.8% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2020-26257?
CVE-2020-26257 has a CVSS v3 base score of 6.5 (NVD). The EG score is currently aggregating — additional source signals are being incorporated as they become available..
How do I remediate CVE-2020-26257?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2020-26257, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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