# CVE-2024-40640: Usage of non-constant time base64 decoder could lead to leakage of secret key material in vodozemac

> An attacker with high-precision timing access could infer secret key material from vodozemac's non-constant time base64 decoder.

- **Severity:** Low 2.9 (`CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Jul 2024
- **Updated:** 2 Aug 2024
- **Also known as:** GHSA-j8cm-g7r6-hfpq, RUSTSEC-2024-0354

## What is CVE-2024-40640?

CVE-2024-40640 is a low-severity vulnerability in matrix-org vodozemac, published on 17 Jul 2024. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

vodozemac is an open source implementation of Olm and Megolm in pure Rust.  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. 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. This has been patched in commit 734b6c6948d4b2bdee3dd8b4efa591d93a61d272 which has been included in release version 0.7.0. Users are advised to upgrade. There are no known workarounds for this vulnerability.

Weakness: CWE-208 (Observable Timing Discrepancy)

## Which versions are affected by CVE-2024-40640?

3 open source packages ship an affected version, including vodozemac.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `vodozemac` | crates.io | All versions | 0.7.0 |
| `vodozemac` | crates.io | All versions | 0.7.0 |
| `vodozemac` | crates.io | From 0.0.0-0 | 0.7.0 |

## How do I fix CVE-2024-40640?

Upgrade vodozemac to 0.7.0 or later.

## Is CVE-2024-40640 being exploited?

There is no known exploitation of CVE-2024-40640 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2024-40640 and fix it if it is affected.

What it is: CVE-2024-40640 is a low-severity vulnerability in matrix-org vodozemac, published on 17 Jul 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2024-40640 in the wild and no public exploit code.

Affected packages and fixed versions:
- vodozemac (crates.io): affected all versions; fixed in 0.7.0
- vodozemac (crates.io): affected all versions; fixed in 0.7.0
- vodozemac (crates.io): affected from 0.0.0-0; fixed in 0.7.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2024-40640/ (Markdown: https://insights.sbomify.com/CVE-2024-40640/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-40640
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-40640
- OSV: https://osv.dev/vulnerability/CVE-2024-40640

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-40640/
Summaries are generated and may contain mistakes; the official description above is the record.