CVE-2022-39246

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CVE-2022-39246

Summary: matrix-android-sdk2 vulnerable to impersonation via forwarded Megolm sessions

Details: matrix-android-sdk2 is the Matrix SDK for Android. Prior to version 1.5.1, an attacker cooperating with a malicious homeserver can construct messages appearing to have come from another person. Such messages will be marked with a grey shield on some platforms, but this may be missing in others. This attack is possible due to the key forwarding strategy implemented in the matrix-android-sdk2 that is too permissive. Starting with version 1.5.1, the default policy for accepting key forwards has been made more strict in the matrix-android-sdk2. The matrix-android-sdk2 will now only accept forwarded keys in response to previously issued requests and only from own, verified devices. The SDK now sets a `trusted` flag on the decrypted message upon decryption, based on whether the key used to decrypt the message was received from a trusted source. Clients need to ensure that messages decrypted with a key with `trusted = false` are decorated appropriately (for example, by showing a warning for such messages). As a workaroubnd, current users of the SDK can disable key forwarding in their forks using `CryptoService#enableKeyGossiping(enable: Boolean)`.

References: https://github.com/matrix-org/matrix-android-sdk2/releases/tag/v1.5.1, https://github.com/CVEProject/cvelistV5/tree/main/cves/2022/39xxx/CVE-2022-39246.json, https://github.com/matrix-org/matrix-android-sdk2/security/advisories/GHSA-2pvj-p485-cp3m, https://nvd.nist.gov/vuln/detail/CVE-2022-39246, https://github.com/matrix-org/matrix-android-sdk2/commit/77df720a238d17308deab83ecaa37f7a4740a17e, https://github.com/matrix-org/matrix-spec-proposals/pull/3061