| Package | Affected versions | Patched versions |
|---|---|---|
| browserify-sign | < 4.2.2 | 4.2.2 |
| browserify-sign | ≥ 2.6.0, < 4.2.2 | 4.2.2 |
An upper bound check issue in dsaVerify function allows an attacker to construct signatures that can be successfully verified by any public key, thus leading to a signature forgery attack.
In dsaVerify function, it checks whether the value of the signature is legal by calling function checkValue, namely, whether r and s are both in the interval [1, q - 1]. However, the second line of the checkValue function wrongly checks the upper bound of the passed parameters, since the value of b.cmp(q) can only be 0, 1 and -1, and it can never be greater than q.
In this way, although the values of s cannot be 0, an attacker can achieve the same effect as zero by setting its value to q, and then send (r, s) = (1, q) to pass the verification of any public key.
All places in this project that involve DSA verification of user-input signatures will be affected by this vulnerability.
Since the temporary private fork was deleted, here's a webarchive of the PR discussion and diff pages: PR webarchive.zip
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