{"id":"CVE-2022-39248","aliases":["GHSA-fpgf-pjjv-2qgm"],"url":"https://o3.security/vulnerability/CVE-2022-39248","summary":"matrix-android-sdk2 vulnerable to Olm/Megolm protocol confusion","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","published":"2022-09-28T20:05:12Z","modified":"2026-10-28T02:30:28.581014155Z","cvss":{"score":8.6,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N"},"epss":{"score":0.00781,"percentile":0.52842,"asOf":"2026-08-23"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Maven","name":"org.matrix.android:matrix-android-sdk2","fixedVersion":"1.5.1"}],"fix":{"url":"https://github.com/matrix-org/matrix-android-sdk2/commit/77df720a238d17308deab83ecaa37f7a4740a17e","label":"matrix-org/matrix-android-sdk2@77df720"},"references":[{"type":"WEB","url":"https://github.com/matrix-org/matrix-android-sdk2/releases/tag/v1.5.1"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2022/39xxx/CVE-2022-39248.json"},{"type":"ADVISORY","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":"FIX","url":"https://github.com/matrix-org/matrix-android-sdk2/commit/77df720a238d17308deab83ecaa37f7a4740a17e"},{"type":"ARTICLE","url":"https://matrix.org/blog/2022/09/28/upgrade-now-to-address-encryption-vulns-in-matrix-sdks-and-clients"},{"type":"PACKAGE","url":"https://github.com/matrix-org/matrix-android-sdk2"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:30:28.581014155Z"}}