Headline
Matrix address flaws that break message encryption assurances
Confidentiality and authentication flaws uncovered by researchers
Emma Woollacott 04 October 2022 at 14:49 UTC
Updated: 04 October 2022 at 16:00 UTC
Confidentiality and authentication flaws uncovered by researchers
Matrix has patched five serious vulnerabilities in its end-to-end encryption that break the confidentiality and authentication of messages.
The flaws would allow a malicious server to read user messages and impersonate devices.
Matrix currently has 69 million accounts in total, spread over around 100,000 servers. The technology provides a federated communication protocol, allowing clients with accounts on different Matrix servers – their homeservers – to exchange messages across the entire ecosystem.
The platform enables end-to-end encryption by default.
However, four researchers – Martin Albrecht of the Royal Holloway, University of London, Sofía Celi of Brave Software, Benjamin Dowling of the University of Sheffield, and Daniel Jones of the University of London – have demonstrated (PDF) five practically-exploitable flaws.
Fairly straightforward
The vulnerabilities, two of which are rated critical, undermine assurances of authentication and confidentiality normally offered by the Matrix platform.
“All our attacks require a malicious homeserver – the server where users create accounts – i.e., no external party could mount them because all Matrix communication between clients and servers and between servers for federation are protected by TLS,” Albrecht told The Daily Swig.
Catch up with the latest encryption-related news and analysis
“Now, for a malicious homeserver, carrying out these attacks would have been easy. We have implemented proof-of-concept attacks for the vulnerabilities we reported, and these [are] usually fairly straightforward.”
The first critical vulnerability, CVE-2022-39250, is key/device identifier confusion in SAS verification, a bug in matrix-js-sdk that confuses device IDs and cross-signing keys. “This could be exploited by a malicious server admin to break emoji-based verification when cross-signing is in use, authenticating themselves rather than the target user,” according to a security notice by the developers of Matrix.
The other critically-rate flaw, CVE-2022-39251, is a protocol-confusion bug that incorrectly accepts to-device messages encrypted by Megolm rather than Olm, attributing them to the Megolm sender rather than the actual sender. The vulnerability potentially allows an attacker to send fake keys in order to spoof historical messages from other users.
In addition, the flaw creates a means to add a malicious key backup to a user’s account in order to exfiltrate message keys. Matrix’s developers said this attack scenario, which would require certain unusual preconditions, has not been detected in the wild.
Impersonation attack
Meanwhile, a semi-trusted impersonation attack exploits a lack of verification in Element in order to send attacker-controlled Megolm sessions to a target device, falsely posing as a session of the device they wish to impersonate.
Another vulnerability allows a malicious homeserver to add users under their control to end-to-end encrypted rooms – where they can then decrypt future messages sent in the room. This happens because room management messages aren’t authenticated in the Matrix specification, meaning they can be faked by a rogue homeserver.
Lastly Matrix’s use of AES-CTR to encrypt attachments, secrets, and symmetric key backups was faulted for lacking cryptographical rigour. Not good but, as the researchers acknowledge, this IND-CCA break falls short of anything that would result in a practical attack.
The researchers conclude that some of the vulnerabilities reside in the Matrix protocol itself, saying that they highlight the need for a systematic and formal analysis of the cryptography in the Matrix standard.
Enter the Matrix
However, the developers of Matrix dispute this.
“We consider the protocol itself to be sound and our security processes to be robust,” Matthew Hodgson, co-founder and project lead for Matrix and CEO/CTO at Element, told The Daily Swig.
“For instance, we’re currently in the middle of a series of public, independent audits of our next-gen SDKs [software development kits] from Least Authority, and it’s worth noting that our next-gen implementations are not vulnerable to the implementation bugs in question here.”
Albrecht responded: “The Matrix developers have shared with us their plans for addressing the issues we argued about, so we are hopeful that eventually the right outcome – Matrix achieving the security guarantees that it promises – will be achieved.”
Element offers the flagship client and prototype implementation of Matrix.
RELATED Let’s Encrypt builds infrastructure to support browser-based certificate revocation revival
Related news
Ubuntu Security Notice 5724-1 - Multiple security issues were discovered in Thunderbird. If a user were tricked into opening a specially crafted website in a browsing context, an attacker could potentially exploit these to cause a denial of service, bypass Content Security Policy or other security restrictions, or execute arbitrary code. These issues only affect Ubuntu 18.04 LTS, Ubuntu 20.04 LTS and Ubuntu 22.04 LTS.
Gentoo Linux Security Advisory 202210-35 - Multiple vulnerabilities have been found in Mozilla Thunderbird, the worst of which could result in arbitrary code execution. Versions less than 102.4.0 are affected.
Red Hat Security Advisory 2022-7184-01 - Mozilla Thunderbird is a standalone mail and newsgroup client. This update upgrades Thunderbird to version 102.4.0. Issues addressed include a denial of service vulnerability.
Red Hat Security Advisory 2022-7183-01 - Mozilla Thunderbird is a standalone mail and newsgroup client. This update upgrades Thunderbird to version 102.4.0. Issues addressed include a denial of service vulnerability.
Red Hat Security Advisory 2022-7181-01 - Mozilla Thunderbird is a standalone mail and newsgroup client. This update upgrades Thunderbird to version 102.4.0. Issues addressed include a denial of service vulnerability.
Red Hat Security Advisory 2022-7178-01 - Mozilla Thunderbird is a standalone mail and newsgroup client. This update upgrades Thunderbird to version 102.4.0. Issues addressed include a denial of service vulnerability.
Red Hat Security Advisory 2022-7190-01 - Mozilla Thunderbird is a standalone mail and newsgroup client. This update upgrades Thunderbird to version 102.4.0. Issues addressed include a denial of service vulnerability.
Red Hat Security Advisory 2022-7182-01 - Mozilla Thunderbird is a standalone mail and newsgroup client. This update upgrades Thunderbird to version 102.4.0. Issues addressed include a denial of service vulnerability.
An update for thunderbird is now available for Red Hat Enterprise Linux 8. Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.This content is licensed under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/). If you distribute this content, or a modified version of it, you must provide attribution to Red Hat Inc. and provide a link to the original. Related CVEs: * CVE-2022-39236: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to a data corruption issue * CVE-2022-39249: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to an impersonation attack by malicious server administrators * CVE-2022-39250: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to a device verification attack * CVE-2022-39251: ...
An update for thunderbird is now available for Red Hat Enterprise Linux 7. Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.This content is licensed under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/). If you distribute this content, or a modified version of it, you must provide attribution to Red Hat Inc. and provide a link to the original. Related CVEs: * CVE-2022-39236: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to a data corruption issue * CVE-2022-39249: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to an impersonation attack by malicious server administrators * CVE-2022-39250: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to a device verification attack * CVE-2022-39251: ...
An update for thunderbird is now available for Red Hat Enterprise Linux 8.4 Extended Update Support. Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.This content is licensed under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/). If you distribute this content, or a modified version of it, you must provide attribution to Red Hat Inc. and provide a link to the original. Related CVEs: * CVE-2022-39236: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to a data corruption issue * CVE-2022-39249: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to an impersonation attack by malicious server administrators * CVE-2022-39250: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to a device verification...
An update for thunderbird is now available for Red Hat Enterprise Linux 8.1 Update Services for SAP Solutions. Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.This content is licensed under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/). If you distribute this content, or a modified version of it, you must provide attribution to Red Hat Inc. and provide a link to the original. Related CVEs: * CVE-2022-39236: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to a data corruption issue * CVE-2022-39249: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to an impersonation attack by malicious server administrators * CVE-2022-39250: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to a device ve...
An update for thunderbird is now available for Red Hat Enterprise Linux 8.2 Extended Update Support. Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.This content is licensed under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/). If you distribute this content, or a modified version of it, you must provide attribution to Red Hat Inc. and provide a link to the original. Related CVEs: * CVE-2022-39236: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to a data corruption issue * CVE-2022-39249: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to an impersonation attack by malicious server administrators * CVE-2022-39250: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to a device verification...
An update for thunderbird is now available for Red Hat Enterprise Linux 9. Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.This content is licensed under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/). If you distribute this content, or a modified version of it, you must provide attribution to Red Hat Inc. and provide a link to the original. Related CVEs: * CVE-2022-39236: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to a data corruption issue * CVE-2022-39249: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to an impersonation attack by malicious server administrators * CVE-2022-39250: Mozilla: Matrix SDK bundled with Thunderbird vulnerable to a device verification attack * CVE-2022-39251: ...
## Impact An attacker cooperating with a malicious homeserver could interfere with the verification flow between two users, injecting its own cross-signing user identity in place of one of the users’ identities, leading to the other device trusting/verifying the user identity under the control of the homeserver instead of the intended one. The vulnerability is a bug in the matrix-js-sdk, caused by checking and signing user identities and devices in two separate steps, and inadequately fixing the keys to be signed between those steps. Even though the attack is partly made possible due to the design decision of treating cross-signing user identities as Matrix devices on the server side (with their device ID set to the public part of the user identity key), no other examined implementations were vulnerable. ## Patches The matrix-js-sdk has been modified to double check that the key signed is the one that was verified instead of just referencing the key by ID. An additional check has ...
### 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. These attacks are possible due to a protocol confusion vulnerability that accepts to-device messages encrypted with Megolm instead of Olm. ### Patches 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: - Cleartext `m.room_key`, `m.forwarded_room_key` and `m.secret.send` to_device messages are discarded. - S...
Matrix iOS SDK allows developers to build iOS apps compatible with Matrix. Prior to version 0.23.19, 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 matrix-ios-sdk implementing a too permissive key forwarding strategy. The default policy for accepting key forwards has been made more strict in the matrix-ios-sdk version 0.23.19. matrix-ios-sdk 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). Thi...
Matrix iOS SDK allows developers to build iOS apps compatible with Matrix. Prior to version 0.23.19, 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 matrix-ios-sdk implementing a too permissive key forwarding strategy. The default policy for accepting key forwards has been made more strict in the matrix-ios-sdk version 0.23.19. matrix-ios-sdk 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). Thi...