GHSA-x4gp-pqpj-f43q is a low-severity (CVSS 2.9) CWE-733 vulnerability in curve25519-dalek. A fix is available for curve25519-dalek — see the affected versions and patch details below.
curve25519-dalek has timing variability in `curve25519-dalek`'s `Scalar29::sub`/`Scalar52::sub`
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 GHSA-x4gp-pqpj-f43q.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-x4gp-pqpj-f43q plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,166 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
curve25519-dalekReal-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
Timing variability of any kind is problematic when working with potentially secret values such as elliptic curve scalars, and such issues can potentially leak private keys and other secrets. Such a problem was recently discovered in curve25519-dalek.
The Scalar29::sub (32-bit) and Scalar52::sub (64-bit) functions contained usage of a mask value inside a loop where LLVM saw an opportunity to insert a branch instruction (jns on x86) to conditionally bypass this code section when the mask value is set to zero as can be seen in godbolt:
- 32-bit (see L106): https://godbolt.org/z/zvaWxzvqv
- 64-bit (see L48): https://godbolt.org/z/PczYj7Pda
A similar problem was recently discovered in the Kyber reference implementation:
https://groups.google.com/a/list.nist.gov/g/pqc-forum/c/hqbtIGFKIpU/m/cnE3pbueBgAJ
As discussed on that thread, one portable solution, which is also used in this PR, is to introduce a volatile read as an optimization barrier, which prevents the compiler from optimizing it away.
The fix can be validated in godbolt here:
- 32-bit: https://godbolt.org/z/jc9j7eb8E
- 64-bit: https://godbolt.org/z/x8d46Yfah
The problem was discovered and the solution independently verified by Alexander Wagner [email protected] and Lea Themint [email protected] using their DATA tool:
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | curve25519-dalek | all versions | 4.1.3cargo update -p curve25519-dalek --precise 4.1.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for curve25519-dalek, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update curve25519-dalek to 4.1.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-x4gp-pqpj-f43q 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.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-x4gp-pqpj-f43q can be triaged on real exposure rather than presence alone.
Tailored to GHSA-x4gp-pqpj-f43q. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-x4gp-pqpj-f43q in your dependencies?
O3 Security finds GHSA-x4gp-pqpj-f43q across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.