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The vulnerability in `filippo.io/edwards25519` resides in the `(Point).MultiScalarMult` method, which performs a multi-scalar multiplication on the Edwards curve . This method fails to properly initialize its receiver (the `Point` object it is called on). If the receiver is an existing point that is not the identity element, the method produces an incorrect result. More critically, if the receiver is an uninitialized point (specifically, the zero value of the `Point` struct), the behavior becomes undefined. In such a scenario, the method could return an invalid point that erroneously compares as equal to any other valid point on the curve, completely breaking the expected group logic. This issue is particularly severe because it undermines the fundamental cryptographic guarantees of the library. However, its practical impact is considered low, as the `MultiScalarMult` API is a rarely used advanced feature. Most users of higher-level packages (like `crypto/ed25519` or github.com/go-sql-driver/mysql) that depend on this library are unaffected. The vulnerability was identified, reviewed, and published to the GitHub Advisory Database, with a fix likely integrated into the latest version of the module .
Platform: filippo.io/edwards25519
Version: Prior to v1.2.0
Vulnerability: MultiScalarMult initialization failure
Severity: Low
Date: Feb 17, 2026
Prediction: Feb 18, 2026
What Undercode Say:
This vulnerability highlights a critical, yet subtle, class of bugs in cryptographic implementations: state-dependent method behavior. The core issue is that the `MultiScalarMult` method does not reset or initialize its receiver, assuming it to be in a clean state (the identity). This leads to two distinct failure modes:
1. Incorrect Computation: If the receiver is any non-identity point, the result of the scalar multiplication is mathematically wrong.
2. Broken Equality Contract: If the receiver is the Go zero value, it returns a special invalid point. This invalid point then breaks the `Equal` method, making it return `true` when compared to any other point. This could allow an attacker to forge proofs or signatures in systems that rely on this low-level library for equality checks.
To check if your project uses an affected version, you can inspect your `go.mod` file:
Check the version of filippo.io/edwards25519 in your go.mod grep filippo.io/edwards25519 go.mod
To update the vulnerable package to the patched version, use:
go get filippo.io/[email protected] go mod tidy
The following Go code demonstrates the undefined behavior with an uninitialized receiver:
package main
import (
"fmt"
"filippo.io/edwards25519"
)
func main() {
// Create two distinct, valid points.
P := edwards25519.NewGeneratorPoint()
Q := edwards25519.NewIdentityPoint()
// Create a zero-value point (uninitialized). This is the vulnerable receiver.
var zeroPoint edwards25519.Point
// Create a dummy scalar (all zeros).
scalar := edwards25519.NewScalar()
// Call MultiScalarMult on the zero-value receiver.
// The behavior is undefined, but we can observe one possible outcome.
result := zeroPoint.MultiScalarMult([]edwards25519.Scalar{scalar}, []edwards25519.Point{P})
// This result might be an invalid point that incorrectly equals Q.
// In a vulnerable version, the following might print "1", indicating equality.
fmt.Println("Is the result equal to the identity?", result.Equal(edwards25519.NewIdentityPoint()))
fmt.Println("Is the result equal to the generator?", result.Equal(edwards25519.NewGeneratorPoint()))
}
Exploit:
A direct exploit is not straightforward, as the issue is a logic flaw rather than an overflow or injection. However, an attacker could craft a scenario where a system uses an uninitialized `Point` as a receiver for MultiScalarMult. For example, if a developer erroneously declares a `Point` variable without using `NewIdentityPoint()` and later uses it in a multi-scalar multiplication, the resulting invalid point could be used to bypass signature checks or verification logic that relies on point equality. The most dangerous outcome is the invalid point comparing equal to any other point, effectively creating a “wildcard” value.
Protection from this CVE
The primary and most effective protection is to update the `filippo.io/edwards25519` module to version 1.2.0 or later, where this issue is fixed.
go get filippo.io/edwards25519@latest
For developers, the fix is to never use the zero value of `Point` as a receiver for any method, especially MultiScalarMult. Always initialize points using `NewIdentityPoint()` or NewGeneratorPoint(). Code reviews should specifically check for uninitialized struct usage in cryptographic contexts.
Impact
CVSS Score: Not formally assigned, but likely low due to the niche API.
Scope: Affects any application directly using the `MultiScalarMult` API of this library with an uninitialized or incorrectly initialized receiver.
Technical Impact: The integrity of cryptographic operations is compromised, leading to incorrect computation results or broken equality comparisons. This could potentially be leveraged to bypass authentication or verification if the flawed logic is integrated into a critical path.
Exploitability: The conditions required to trigger the vulnerability (using an uninitialized point with a specific advanced method) are unlikely in typical use cases, making it difficult to exploit in the wild.
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Sources:
Reported By: github.com
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