CVE-2021-21393Medium· 5.3▾ SunlitDenial of service (via resource exhaustion) due to improper input validation on groups/communities endpoints
▾ Sunlit zone — Low / medium · no exploitation signal
impact 29.2 · 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
1.6%
Missing input validation of some parameters on the groups (also known as communities) endpoints could cause excessive use of disk space and memory leading to resource exhaustion. Additionally clients may have issues rendering large fields.
This issue is fixed by #9321 and #9393.
The groups feature can be disabled (by setting enable_group_creation to False) to mitigate this issue. Note that it is disabled by default.
Note that the groups feature is not part of the Matrix specification and the chosen maximum lengths are arbitrary. Not all clients might abide by them.
matrix-synapse < 1.28.0Upgrade to a patched release:
matrix-synapse 1.28.0Connected by shared product, vendor, weakness, or advisory.
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