CVE-2021-41281

Published: 23 November 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 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.

Priority

Cvss 3 Severity Score

7.5

Score breakdown

Status

Package	Release	Status
matrix-synapse Launchpad, Ubuntu, Debian	bionic	Needed
	focal	Needed
	hirsute	Ignored (end of life)
	impish	Ignored (end of life)
	jammy	Needed
	kinetic	Ignored (end of life, was needed)
	lunar	Not vulnerable (1.64.0-3)
	mantic	Not vulnerable (1.64.0-3)
	trusty	Ignored (end of standard support)
	upstream	Released (1.47.1-1)
	xenial	Ignored (end of standard support)

Severity score breakdown

Parameter	Value
Base score	7.5
Attack vector	Network
Attack complexity	Low
Privileges required	None
User interaction	None
Scope	Unchanged
Confidentiality	None
Integrity impact	High
Availability impact	None
Vector	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

References

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