CVE-2021-41281
No exploitation reported by the sources we read.
- Published2021-11-23
- WeaknessCWE-22
Am I affected?
Debian, Ubuntu or Red Hat sometimes backport a fix without changing the upstream version number: such a version reads « to verify », never « affected ».With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.
Description
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.
Timeline
dates in UTC- 2021-11-2320:15CVE publishedNVD
Observed activity
isMalicious corpus · updated 2026-10-23 18:48 UTCBlock these indicators
- Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-41281?format=txt
- CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-41281?format=csv
- TAXII collection of exploited CVEs
- The EDL and CSV take an API key on the Pro plan.
Versions per branch
NVD| Branch | Affected | Fixed in | Source |
|---|---|---|---|
| 34.x | = 34 | no fix published | NVD |
| 35.x | = 35 | no fix published | NVD |
| Branch | Affected | Fixed in | Source |
|---|---|---|---|
| 1.47 | < 1.47.1 | 1.47.1 | NVD |
as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.
Fix
Advisories and patches
- github.comPatch
- github.comRelease Notes
- github.comMitigation
Detection
- Nuclei template
- none so far ProjectDiscovery
- Exploit-DB
- no entry Exploit-DB
- Proof-of-concept repositories
- none listed PoC-in-GitHub
Sources
- CNACVSS 3.17.5read 2026-10-23
- NVDCVSS 2.04.3read 2026-10-23
- CNAweakness (CWE)CWE-22read 2026-10-23
- NVDweakness (CWE)CWE-22read 2026-10-23
- FIRST EPSSEPSS score1.6 %2026-10-22
Technical details
- CVSS v3 Vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- Published
- 2021-11-23
- Last Modified
- 2026-06-17
- NVD status
- Modified
Frequently asked questions
What is CVE-2021-41281?
Is CVE-2021-41281 actively exploited?
What is the CVSS score for CVE-2021-41281?
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