GHSA-xx36-6rv4-gj8r is a critical-severity (CVSS 9.8) CWE-347 vulnerability in ecdsa-elixir. 1 public exploit reference exists, so weaponization risk is real. A fix is available for ecdsa-elixir — see the affected versions and patch details below.
ecdsa-elixir fails to check signatures, vulnerable to message forging
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-xx36-6rv4-gj8r 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
ecdsa-elixirReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Hex packages — download data is not available via public APIs for these ecosystems.
Description
Summary
Stark Bank is a financial technology company that provides services to simplify and automate digital banking, by providing APIs to perform operations such as payments and transfers. In addition, Stark Bank maintains a number of cryptographic libraries to perform cryptographic signing and verification. These popular libraries are meant to be used to integrate with the Stark Bank ecosystem, but are also accessible on popular package manager platforms in order to be used by other projects. The node package manager reports around 16k weekly downloads for the ecdsa-node implementation while the Python implementation boasts over 7.3M downloads in the last 90 days on PyPI. A number of these libraries suffer from a vulnerability in the signature verification functions, allowing attackers to forge signatures for arbitrary messages which successfully verify with any public key.
Impact
An attacker can forge signatures on arbitrary messages that will verify for any public key. This may allow attackers to authenticate as any user within the Stark Bank platform, and bypass signature verification needed to perform operations on the platform, such as send payments and transfer funds. Additionally, the ability for attackers to forge signatures may impact other users and projects using these libraries in different and unforeseen ways.
Details
The (slightly simplified) ECDSA verification of a signature (r, s) on a hashed message z with public key Q and curve order n works as follows:
The (slightly simplified) ECDSA verification of a signature (r, s) on a hashed message z with public key Q and curve order n works as follows:
- Check that r and s are integers in the [1, n-1] range, return Invalid if not.
- Compute u<sub>1</sub> = zs<sup>-1</sup> mod n and u<sub>2</sub> = rs<sup>-1</sup> mod n.
- Compute the elliptic curve point (x, y) = u<sub>1</sub>G + u<sub>2</sub>Q, return Invalid if (x, y) is the point at infinity.
- Return Valid if r ≡ x mod n, Invalid otherwise.
The ECDSA signature verification functions in the libraries listed above fail to perform the first check, ensuring that the r and s components of the signatures are in the correct range. Specifically, the libraries are not checking that the components of the signature are non-zero, which is an important check mandated by the standard, see X9.62:2005, Section 7.4.1/a:
- If r’ is not an integer in the interval [1, n-1], then reject the signature.
- If s’ is not an integer in the interval [1, n-1], then reject the signature.
For example, consider the following excerpt of the verify function from the ecdsa-python implementation.
def verify(cls, message, signature, publicKey, hashfunc=sha256):
byteMessage = hashfunc(toBytes(message)).digest()
numberMessage = numberFromByteString(byteMessage)
curve = publicKey.curve
r = signature.r
s = signature.s
inv = Math.inv(s, curve.N)
u1 = Math.multiply(curve.G, n=(numberMessage * inv) % curve.N, N=curve.N, A=curve.A, P=curve.P)
u2 = Math.multiply(publicKey.point, n=(r * inv) % curve.N, N=curve.N, A=curve.A, P=curve.P)
add = Math.add(u1, u2, A=curve.A, P=curve.P)
modX = add.x % curve.N
return r == modX
In that code snippet, the values r and s are extracted from the signature without any range check. An attacker supplying a signature equal to (r, s) = (0, 0) will not see their signature rejected. Proceeding with the verification, this function computes the inverse of the s component. Note that the Math.inv() function returns zero when supplied with a zero input (even though 0 does not admit an inverse). The code then computes the values u1 = inv * numberMessage * G and u2 = inv * r * Q, but since inv is zero, u1 and u2 will both be zero, i.e., the point at infinity, regardless of the value of numberMessage (the message hash, which we called z above) and Q (the public key). Subsequently, the implementation computes the intermediary curve point add by adding up the two previously computed points, which again results in the point at infinity. The final line checks that the r-component of the signature is equal to the x-coordinate of the curve point, essentially checking that 0 == 0 for all any message and any public key. Therefore, a signature (r, s) = (0, 0) is deemed valid by the code for any message, and under any public key.
Recommendation
Users of the different Stark Bank ECDSA libraries should update to the latest versions. Specifically, versions larger or at least equal to the following should be used.
- ecdsa-python: v2.0.1
- ecdsa-java: v1.0.1
- ecdsa-dotnet: v1.3.2
- ecdsa-elixir v1.0.1
- ecdsa-node v1.1.3
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💧Hex | ecdsa-elixir | ≥ 1.0.0&&< 1.0.1 | 1.0.1mix deps.update ecdsa-elixir |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ecdsa-elixir, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update ecdsa-elixir to 1.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-xx36-6rv4-gj8r 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-xx36-6rv4-gj8r can be triaged on real exposure rather than presence alone.
Tailored to GHSA-xx36-6rv4-gj8r. 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-xx36-6rv4-gj8r in your dependencies?
O3 Security finds GHSA-xx36-6rv4-gj8r across Hex dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.