CVE-2020-26257

MEDIUMNVD 6.56.5—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.5 under NVD CVSS v3. EPSS exploit probability: 2.4% (83rd percentile of EPSS-scored CVEs). 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: epss, nvd
6.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 2.4%CVSS: 6.5Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

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
6.5MEDIUMmedium confidence
EG Risk
35
EG Risk 35/100CISA SSVC

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity65% × 45%
Exploitation2% × 40%
Automatability30% × 15%
CISA SSVC: Track at low or medium mission impact; Track or Attend at high (mission-essential systems).
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
2.4%
EPSS %ILE
83rd
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track or Attend at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation none (no KEV listing, exploit record or EPSS ≥ 50%) · Automatable unknown (not published for this CVE) · Technical impact partial (CVSS below 9.0). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

December 9, 2020

Last Modified

November 21, 2024

References (12)

Affected Packages

(2 across 2 ecosystems)
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
matrix-synapse0.19.2+dfsg-3 ... 1.9.1-1~bpo10+1 (135 versions)
  • every version up to 1.24.0-1: fixed in 1.24.0-1
—
PyPI(1)
PackageVulnerable rangeFix by version rangeDependents
matrix-synapse0.33.5 ... 1.9.1 (138 versions)
  • every version up to 1.23.1: fixed in 1.23.1
—

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 8× in last 7d / 26× 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.

Showing the most recent 100 of 161 total refreshes for this CVE.

  1. 2026-10-09 20:04 UTCEPSS rescore
  2. 2026-10-09 12:55 UTCOSV refresh
  3. 2026-10-08 16:38 UTCEPSS rescore
  4. 2026-10-07 23:44 UTCEPSS rescore
  5. 2026-10-06 15:13 UTCEPSS rescore
  6. 2026-10-05 17:39 UTCEPSS rescore
  7. 2026-10-04 23:18 UTCEPSS rescore
  8. 2026-10-03 14:22 UTCEPSS rescore
  9. 2026-09-30 15:16 UTCEG score recompute
  10. 2026-09-30 14:59 UTCEPSS rescore
  11. 2026-09-29 15:14 UTCEPSS rescore
  12. 2026-09-27 13:41 UTCEPSS rescore
  13. 2026-09-26 15:54 UTCEPSS rescore
  14. 2026-09-26 15:54 UTCEPSS rescore
  15. 2026-09-24 14:00 UTCEPSS rescore
  16. 2026-09-22 14:43 UTCEPSS rescore
  17. 2026-09-21 20:28 UTCEPSS rescore
  18. 2026-09-19 20:03 UTCOSV refresh
  19. 2026-09-19 15:37 UTCEPSS rescore
  20. 2026-09-18 19:23 UTCEPSS rescore
  21. 2026-09-17 19:22 UTCEPSS rescore
  22. 2026-09-16 14:04 UTCEPSS rescore
  23. 2026-09-15 03:06 UTCEPSS rescore
  24. 2026-09-13 16:43 UTCEPSS rescore
  25. 2026-09-12 14:57 UTCEPSS rescore
Show 75 more
  1. 2026-09-11 09:32 UTCEPSS rescore
  2. 2026-09-08 21:56 UTCEPSS rescore
  3. 2026-09-07 15:57 UTCEPSS rescore
  4. 2026-09-06 13:44 UTCEPSS rescore
  5. 2026-09-05 15:24 UTCEPSS rescore
  6. 2026-09-04 13:57 UTCEPSS rescore
  7. 2026-09-04 05:03 UTCEPSS rescore
  8. 2026-09-02 14:08 UTCEPSS rescore
  9. 2026-09-01 03:32 UTCEPSS rescore
  10. 2026-08-31 23:34 UTCOSV refresh
  11. 2026-08-30 19:14 UTCEPSS rescore
  12. 2026-08-30 01:18 UTCEPSS rescore
  13. 2026-08-27 14:21 UTCEPSS rescore
  14. 2026-08-26 14:42 UTCEPSS rescore
  15. 2026-08-25 13:45 UTCEPSS rescore
  16. 2026-08-21 23:45 UTCEPSS rescore
  17. 2026-08-20 22:52 UTCEPSS rescore
  18. 2026-08-19 17:00 UTCEPSS rescore
  19. 2026-08-18 13:44 UTCEPSS rescore
  20. 2026-08-17 13:43 UTCEPSS rescore
  21. 2026-08-16 14:52 UTCEPSS rescore
  22. 2026-08-16 02:11 UTCEPSS rescore
  23. 2026-08-15 01:26 UTCEPSS rescore
  24. 2026-08-15 00:24 UTCOSV refresh
  25. 2026-08-13 21:57 UTCEPSS rescore
  26. 2026-08-12 13:47 UTCEPSS rescore
  27. 2026-08-08 16:33 UTCEPSS rescore
  28. 2026-08-07 16:23 UTCEPSS rescore
  29. 2026-08-06 13:43 UTCEPSS rescore
  30. 2026-08-04 15:06 UTCEPSS rescore
  31. 2026-08-04 10:34 UTCEPSS rescore
  32. 2026-08-02 02:23 UTCEPSS rescore
  33. 2026-08-01 04:12 UTCEPSS rescore
  34. 2026-07-30 16:25 UTCEPSS rescore
  35. 2026-07-30 13:14 UTCOSV refresh
  36. 2026-07-30 01:27 UTCEPSS rescore
  37. 2026-07-28 15:33 UTCEPSS rescore
  38. 2026-07-26 14:51 UTCEPSS rescore
  39. 2026-07-25 14:15 UTCEPSS rescore
  40. 2026-07-24 14:14 UTCEPSS rescore
  41. 2026-07-23 14:15 UTCEPSS rescore
  42. 2026-07-23 14:15 UTCEPSS rescore
  43. 2026-07-23 01:51 UTCEG score recompute
  44. 2026-07-22 22:37 UTCEG score recompute
  45. 2026-07-22 14:05 UTCEPSS rescore
  46. 2026-07-21 15:22 UTCEPSS rescore
  47. 2026-07-21 15:22 UTCEPSS rescore
  48. 2026-07-20 17:04 UTCEPSS rescore
  49. 2026-07-20 17:04 UTCEPSS rescore
  50. 2026-07-19 14:28 UTCEPSS rescore
  51. 2026-07-19 14:28 UTCEPSS rescore
  52. 2026-07-19 02:26 UTCEPSS rescore
  53. 2026-07-19 02:26 UTCEPSS rescore
  54. 2026-07-16 16:59 UTCEPSS rescore
  55. 2026-07-15 16:55 UTCEPSS rescore
  56. 2026-07-15 16:55 UTCEPSS rescore
  57. 2026-07-15 01:57 UTCEPSS rescore
  58. 2026-07-13 22:27 UTCEPSS rescore
  59. 2026-07-13 22:27 UTCEPSS rescore
  60. 2026-07-13 06:10 UTCEPSS rescore
  61. 2026-07-13 06:10 UTCEPSS rescore
  62. 2026-07-12 22:08 UTCOSV refresh
  63. 2026-07-12 05:44 UTCEPSS rescore
  64. 2026-07-11 08:25 UTCEPSS rescore
  65. 2026-07-11 08:25 UTCEPSS rescore
  66. 2026-07-09 19:07 UTCEPSS rescore
  67. 2026-07-08 15:12 UTCEPSS rescore
  68. 2026-07-07 13:43 UTCEPSS rescore
  69. 2026-07-06 16:25 UTCEPSS rescore
  70. 2026-07-06 16:25 UTCEPSS rescore
  71. 2026-07-06 02:21 UTCEPSS rescore
  72. 2026-07-06 02:21 UTCEPSS rescore
  73. 2026-07-04 06:29 UTCEPSS rescore
  74. 2026-07-04 06:29 UTCEPSS rescore
  75. 2026-06-30 23:20 UTCEPSS rescore

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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 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 2.4% probability of exploitation in the next 30 days (83rd percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2020-26257?
CVE-2020-26257 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2020-26257?
A fix for CVE-2020-26257 is available: update to the fixed version the vendor names in its advisory.

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