GHSA-FPGF-PJJV-2QGM
Vulnerability from github – Published: 2022-09-30 04:37 – Updated: 2022-09-30 04:37Impact
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
Blog post: https://matrix.org/blog/2022/09/28/upgrade-now-to-address-encryption-vulns-in-matrix-sdks-and-clients
For more information
If you have any questions or comments about this advisory, e-mail us at security@matrix.org.
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 1.4.36"
},
"package": {
"ecosystem": "Maven",
"name": "org.matrix.android:matrix-android-sdk2"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.5.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2022-39248"
],
"database_specific": {
"cwe_ids": [
"CWE-287",
"CWE-322"
],
"github_reviewed": true,
"github_reviewed_at": "2022-09-30T04:37:39Z",
"nvd_published_at": "2022-09-28T20:15:00Z",
"severity": "HIGH"
},
"details": "### Impact\nAn 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. \n\nAdditionally, 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.\n\nThese attacks are possible due to a protocol confusion vulnerability that accepts to-device messages encrypted with Megolm instead of Olm.\n\n### Patches\n\nmatrix-android-sdk2 has been modified to only accept Olm-encrypted to-device messages and to stop signing backups on a successful decryption.\n\nOut of caution, several other checks have been audited or added:\n- Cleartext `m.room_key`, `m.forwarded_room_key` and `m.secret.send` to_device messages are discarded.\n- Secrets received from untrusted devices are discarded.\n- Key backups are only usable if they have a valid signature from a trusted device (no more local trust, or trust-on-decrypt).\n- 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.\n\n\n### Workarounds\n\nAs 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.\n\nWe 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.\n\nAs 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.\n\n\n### References\nBlog post: https://matrix.org/blog/2022/09/28/upgrade-now-to-address-encryption-vulns-in-matrix-sdks-and-clients\n\n### For more information\nIf you have any questions or comments about this advisory, e-mail us at [security@matrix.org](mailto:security@matrix.org).\n",
"id": "GHSA-fpgf-pjjv-2qgm",
"modified": "2022-09-30T04:37:39Z",
"published": "2022-09-30T04:37:39Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/matrix-org/matrix-android-sdk2/security/advisories/GHSA-fpgf-pjjv-2qgm"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2022-39248"
},
{
"type": "WEB",
"url": "https://github.com/matrix-org/matrix-android-sdk2/commit/77df720a238d17308deab83ecaa37f7a4740a17e"
},
{
"type": "PACKAGE",
"url": "https://github.com/matrix-org/matrix-android-sdk2"
},
{
"type": "WEB",
"url": "https://github.com/matrix-org/matrix-android-sdk2/releases/tag/v1.5.1"
},
{
"type": "WEB",
"url": "https://matrix.org/blog/2022/09/28/upgrade-now-to-address-encryption-vulns-in-matrix-sdks-and-clients"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N",
"type": "CVSS_V3"
}
],
"summary": "matrix-android-sdk2 vulnerable to Olm/Megolm protocol confusion"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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