CVE-2022-39251 in matrix-js-sdk
Summary
by MITRE • 09/29/2022
Matrix Javascript SDK is the Matrix Client-Server SDK for JavaScript. Prior to version 19.7.0, 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. These attacks are possible due to a protocol confusion vulnerability that accepts to-device messages encrypted with Megolm instead of Olm. Starting with version 19.7.0, matrix-js-sdk has been modified to only accept Olm-encrypted to-device messages. Out of caution, several other checks have been audited or added. This attack requires coordination between a malicious home server and an attacker, so those who trust their home servers do not need a workaround.
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Analysis
by VulDB Data Team • 10/15/2024
The Matrix Javascript SDK vulnerability CVE-2022-39251 represents a critical protocol confusion issue that undermines the security assurances of end-to-end encrypted messaging within the Matrix communication protocol. This vulnerability affects versions prior to 19.7.0 and stems from an improper validation mechanism that accepts to-device messages encrypted with the Megolm encryption protocol instead of the expected Olm protocol. The flaw creates a fundamental breach in the cryptographic integrity of message authentication, allowing malicious actors to forge messages that appear legitimate while maintaining the appearance of authentic user communication. The vulnerability operates through a sophisticated attack vector that requires coordination between a malicious homeserver and an external attacker, leveraging the trust relationship between users and their homeserver infrastructure.
The technical implementation of this vulnerability exploits the protocol confusion by accepting messages that should only be processed when encrypted using Olm encryption, which is specifically designed for to-device messages and provides proper user authentication guarantees. When the SDK processes Megolm-encrypted messages in contexts where Olm encryption is expected, it fails to validate the encryption type properly, allowing malicious actors to bypass the normal authentication checks that would normally prevent message spoofing. This misconfiguration creates a window where an attacker can inject malicious content into the communication stream, potentially compromising the security of key exchange mechanisms and device verification processes. The vulnerability specifically targets the to-device message handling system, which is critical for maintaining secure communication between users' devices and the Matrix homeserver infrastructure.
The operational impact of this vulnerability extends beyond simple message spoofing to enable sophisticated targeted attacks that can compromise user security during critical authentication processes. An attacker can exploit this vulnerability to inject key backup secrets during self-verification procedures, effectively allowing the malicious homeserver to manipulate a user's device into accepting compromised encryption keys. This creates a pathway for man-in-the-middle attacks where users might unknowingly trust malicious encryption keys that appear to originate from legitimate sources. The attack's effectiveness relies on the coordinated efforts of both a malicious homeserver and an external attacker, but the damage potential is significant as it can undermine the fundamental security guarantees that end-to-end encryption is designed to provide. The vulnerability demonstrates a failure in proper protocol validation and encryption type verification within the SDK's message processing pipeline.
The mitigation implemented in version 19.7.0 addresses this vulnerability by enforcing strict validation of encryption protocols for to-device messages, ensuring that only Olm-encrypted messages are accepted in contexts where such encryption is required. This fix aligns with security best practices for cryptographic protocol implementation and follows the principle of least privilege by restricting message processing to only those encryption methods that provide the necessary security guarantees. Additional security checks were implemented as a precautionary measure to prevent similar issues from arising in other areas of the SDK's functionality. The vulnerability's classification under CWE-295 (Improper Certificate Validation) and its alignment with ATT&CK technique T1552.001 (Credentials in Files) reflects the nature of the security breach and the potential for credential compromise through message manipulation. Users who trust their homeserver infrastructure are not directly affected by this vulnerability, but the broader ecosystem remains at risk due to the potential for coordinated attacks that exploit the trust relationships within the Matrix protocol.