CVE-2021-41281

HIGHNVD 7.57.5
EchelonGraph scoreLOW confidence

This high-severity CVE scores 7.5 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
7.5
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 2%CVSS: 7.5Exploit: NoneExposed: 0

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

Synapse is a package for Matrix homeservers written in Python 3/Twisted. Prior to version 1.47.1, Synapse instances with the media repository enabled can be tricked into downloading a file from a remote server into an arbitrary directory. No authentication is required for the affected endpoint. The last 2 directories and file name of the path are chosen randomly by Synapse and cannot be controlled by an attacker, which limits the impact. Homeservers with the media repository disabled are unaffected. Homeservers with a federation whitelist are also unaffected, since Synapse will check the remote hostname, including the trailing ../s, against the whitelist. Server administrators should upgrade to 1.47.1 or later. Server administrators using a reverse proxy could, at the expense of losing media functionality, may block the certain endpoints as a workaround. Alternatively, non-containerized deployments can be adapted to use the hardened systemd config.

CVSS v3
7.5
EG Score
7.5(low)
EPSS
71.5%
KEV
Not listed

Published

November 23, 2021

Last Modified

November 21, 2024

References (10)

Affected Packages

(1 across 1 ecosystem)
PyPI(1)
PackageVulnerable rangeFixed inDependents
matrix-synapse0.33.5 ... 1.9.1 (218 versions)1.47.1—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 9× in last 7d / 48× 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
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  24. 2026-06-25 13:48 UTCEPSS rescore
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  1. 2026-06-24 14:03 UTCEPSS rescore
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  3. 2026-06-24 14:01 UTCOSV refresh
  4. 2026-06-23 21:31 UTCEPSS rescore
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  6. 2026-06-21 14:55 UTCEPSS rescore
  7. 2026-06-21 01:58 UTCEPSS rescore
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  9. 2026-06-19 19:24 UTCEPSS rescore
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  11. 2026-06-18 17:51 UTCEPSS rescore
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  23. 2026-06-12 23:10 UTCEPSS rescore
  24. 2026-06-11 13:58 UTCEPSS rescore
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  26. 2026-06-10 22:16 UTCEPSS rescore
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  28. 2026-06-10 13:20 UTCEPSS rescore
  29. 2026-06-08 14:15 UTCEPSS rescore
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  31. 2026-06-07 18:16 UTCOSV refresh
  32. 2026-06-07 15:23 UTCEPSS rescore
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  41. 2026-06-02 20:11 UTCEPSS rescore
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  43. 2026-05-31 22:29 UTCEPSS rescore
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  45. 2026-05-31 00:15 UTCEPSS rescore
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  47. 2026-05-29 13:42 UTCEPSS rescore
  48. 2026-05-28 13:43 UTCEPSS rescore
  49. 2026-05-28 13:43 UTCEPSS rescore
  50. 2026-05-27 13:39 UTCEPSS rescore
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  52. 2026-05-26 13:42 UTCEPSS rescore
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  54. 2026-05-26 07:17 UTCEPSS rescore
  55. 2026-05-26 07:17 UTCEPSS rescore
  56. 2026-05-26 07:17 UTCEPSS rescore
  57. 2026-05-23 08:31 UTCEG score recompute

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2021-41281?
CVE-2021-41281 is a high vulnerability published on November 23, 2021. Synapse is a package for Matrix homeservers written in Python 3/Twisted. Prior to version 1.47.1, Synapse instances with the media repository enabled can be tricked into downloading a file from a remote server into an arbitrary directory. No authentication is required for the affected endpoint. The…
When was CVE-2021-41281 disclosed?
CVE-2021-41281 was first published in the National Vulnerability Database on November 23, 2021, 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-2021-41281 actively exploited?
CVE-2021-41281 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 71.5% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-41281?
CVE-2021-41281 has a CVSS v3 base score of 7.5 (NVD). The EG score is currently aggregating — additional source signals are being incorporated as they become available..
How do I remediate CVE-2021-41281?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-41281, 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.

Dependency Blast Radius

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