[MAVEN:GHSA-FPGF-PJJV-2QGM] matrix-android-sdk2 vulnerable to Olm/Megolm protocol confusion
Impact
An attacker cooperating with a malicious homeserver can construct messages that legitimately appear to have come from another person, without any indication such as a grey shield.
Additionally, a sophisticated attacker cooperating with a malicious homeserver could employ this vulnerability to perform a targeted attack in order to send fake to-device messages appearing to originate from another user. This can allow, for example, to inject the key backup secret during a self-verification, to make a targeted device start using a malicious key backup spoofed by the homeserver. matrix-android-sdk2 would then additionally sign such a key backup with its device key, spilling trust over to other devices trusting the matrix-android-sdk2 device.
These attacks are possible due to a protocol confusion vulnerability that accepts to-device messages encrypted with Megolm instead of Olm.
Patches
matrix-android-sdk2 has been modified to only accept Olm-encrypted to-device messages and to stop signing backups on a successful decryption.
Out of caution, several other checks have been audited or added:
- Cleartext m.room_key
, m.forwarded_room_key
and m.secret.send
to_device messages are discarded.
- Secrets received from untrusted devices are discarded.
- Key backups are only usable if they have a valid signature from a trusted device (no more local trust, or trust-on-decrypt).
- The origin of a to-device message should only be determined by observing the Olm session which managed to decrypt the message, and not by using claimed sender_key, user_id, or any other fields controllable by the homeserver.
Workarounds
As this attack requires coordination between a malicious home server and an attacker, if you trust your home server no particular workaround is needed. Notice that the backup spoofing attack is a particularly sophisticated targeted attack.
We are not aware of this attack being used in the wild, though specifying a false positive-free way of noticing malicious key backups key is challenging.
As an abundance of caution, to avoid malicious backup attacks, you should not verify your new logins using emoji/QR verifications methods until patched. Prefer using verify with passphrase.
References
For more information
If you have any questions or comments about this advisory, e-mail us at security@matrix.org.
Package | Affected Version |
---|---|
pkg:maven/org.matrix.android/matrix-android-sdk2 | <= 1.4.36 |
Package | Fixed Version |
---|---|
pkg:maven/org.matrix.android/matrix-android-sdk2 | = 1.5.1 |
- ID
- MAVEN:GHSA-FPGF-PJJV-2QGM
- Severity
- high
- URL
- https://github.com/advisories/GHSA-fpgf-pjjv-2qgm
- Published
-
2022-09-30T04:37:39
(23 months ago) - Modified
-
2023-01-29T05:05:16
(19 months ago) - Rights
- Maven Security Team
Type | Package URL | Namespace | Name / Product | Version | Distribution / Platform | Arch | Patch / Fix |
---|---|---|---|---|---|---|---|
Affected | pkg:maven/org.matrix.android/matrix-android-sdk2 | org.matrix.android | matrix-android-sdk2 | <= 1.4.36 | |||
Fixed | pkg:maven/org.matrix.android/matrix-android-sdk2 | org.matrix.android | matrix-android-sdk2 | = 1.5.1 |
# CVE | Description | CVSS | EPSS | EPSS Trend (30 days) | Affected Products | Weaknesses | Security Advisories | Exploits | PoC | Pubblication Date | Modification Date |
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# CVE | Description | CVSS | EPSS | EPSS Trend (30 days) | Affected Products | Weaknesses | Security Advisories | PoC | Pubblication Date | Modification Date |