CVE-2024-40640

vodozemac's usage of non-constant time base64 decoder could lead to leakage of secret key material

Versions before 0.7.0 of vodozemac use a non-constant time base64 implementation for importing key material for Megolm group sessions and PkDecryption Ed25519 secret keys. This flaw might allow an attacker to infer some information about the secret key material through a side-channel attack.

Workarounds

None.

References

A detailed description of the precise attack can be found at https://arxiv.org/abs/2108.04600. We kindly thank Soatok for pointing out this research to us.

For more information

If you have any questions or comments about this advisory please email us at security at matrix.org.

The use of a non-constant time base64 implementation might allow an attacker to observe timing variations in the encoding and decoding operations of the secret key material. This could potentially provide insights into the underlying secret key material.

The impact of this vulnerability is considered low because exploiting the attacker is required to have access to high precision timing measurements, as well as repeated access to the base64 encoding or decoding processes. Additionally, the estimated leakage amount is bounded and low according to the referenced paper.

CVE-2024-40640 has a CVSS score of 3.7 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.7.0); upgrading removes the vulnerable code path.

Kodem intelligence

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The patch is in commit 734b6c6948d4b2bdee3dd8b4efa591d93a61d272.

1. What is CVE-2024-40640? CVE-2024-40640 is a medium-severity security vulnerability in vodozemac (rust), affecting versions < 0.7.0. It is fixed in 0.7.0.
2. How severe is CVE-2024-40640? CVE-2024-40640 has a CVSS score of 3.7 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of vodozemac are affected by CVE-2024-40640? vodozemac (rust) versions < 0.7.0 is affected.
4. Is there a fix for CVE-2024-40640? Yes. CVE-2024-40640 is fixed in 0.7.0. Upgrade to this version or later.
5. Is CVE-2024-40640 exploitable, and should I be worried? Whether CVE-2024-40640 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2024-40640 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2024-40640? Upgrade vodozemac to 0.7.0 or later.

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