CVE-2024-40640 is a low-severity (CVSS 2.9) CWE-208 vulnerability in vodozemac. A fix is available for vodozemac — see the affected versions and patch details below.
Usage of non-constant time base64 decoder could lead to leakage of secret key material in vodozemac
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2024-40640.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
vodozemacReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
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.
Impact
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.
Patches
The patch is in commit 734b6c6948d4b2bdee3dd8b4efa591d93a61d272.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | vodozemac | all versions | 0.7.0cargo update -p vodozemac --precise 0.7.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for vodozemac, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update vodozemac to 0.7.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2024-40640 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2024-40640 in your dependencies?
Find it across crates.io, including transitive dependencies.