CVE-2021-41281High· 7.5▾ TwilightPath traversal in Matrix Synapse
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 41.3 · likelihood 0.3 · exploitation 0
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Exploit-prediction probability, daily snapshots since Jul 8.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via OSV
Last analysed / modified upstream
1.5%
1.5% → 1.6%
Synapse instances with the media repository enabled can be tricked into downloading a file from a remote server into an arbitrary directory, potentially outside the media store directory.
The last two 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 configured with a federation whitelist are also unaffected.
Server administrators should upgrade to 1.47.1 or later.
Server administrators using a reverse proxy could, at the expense of losing media functionality, block the following endpoints:
/_matrix/media/r0/download/{serverName}/{mediaId}/_matrix/media/r0/download/{serverName}/{mediaId}/{fileName}/_matrix/media/r0/thumbnail/{serverName}/{mediaId}Alternatively, non-containerized deployments can be adapted to use the hardened systemd config, located at contrib/systemd/override-hardened.conf.
n/a
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matrix-synapse < 1.47.1Upgrade to a patched release:
matrix-synapse 1.47.1Connected by shared product, vendor, weakness, or advisory.
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