CWE-347
AllowedImproper Verification of Cryptographic Signature
Abstraction: Base · Status: Draft
The product does not verify, or incorrectly verifies, the cryptographic signature for data.
1142 vulnerabilities reference this CWE, most recent first.
GHSA-XX36-6RV4-GJ8R
Vulnerability from github – Published: 2022-05-24 19:20 – Updated: 2023-09-27 21:49Summary
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 u1 = zs-1 mod n and u2 = rs-1 mod n.
- Compute the elliptic curve point (x, y) = u1G + u2Q, 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": [
{
"package": {
"ecosystem": "Hex",
"name": "ecdsa-elixir"
},
"ranges": [
{
"events": [
{
"introduced": "1.0.0"
},
{
"fixed": "1.0.1"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.0.0"
]
}
],
"aliases": [
"CVE-2021-43568"
],
"database_specific": {
"cwe_ids": [
"CWE-347"
],
"github_reviewed": true,
"github_reviewed_at": "2022-07-01T17:15:25Z",
"nvd_published_at": "2021-11-09T22:15:00Z",
"severity": "CRITICAL"
},
"details": "### Summary\nStark 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](https://www.npmjs.com/package/starkbank-ecdsa ) implementation while the Python implementation boasts over [7.3M downloads in the last 90 days on PyPI](https://package.wiki/starkbank-ecdsa). 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.\n\n### Impact\nAn 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.\n\n### Details\nThe (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:\n\nThe (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:\n\n- Check that _**r**_ and _**s**_ are integers in the _**[1, n-1]**_ range, return Invalid if not.\n- Compute _**u\u003csub\u003e1\u003c/sub\u003e = zs\u003csup\u003e-1\u003c/sup\u003e mod n**_ and _**u\u003csub\u003e2\u003c/sub\u003e = rs\u003csup\u003e-1\u003c/sup\u003e mod n**_.\n- Compute the elliptic curve point _**(x, y) = u\u003csub\u003e1\u003c/sub\u003eG + u\u003csub\u003e2\u003c/sub\u003eQ**_, return Invalid if _**(x, y)**_ is the point at infinity.\n- Return Valid if _**r \u2261 x mod n**_, Invalid otherwise.\n\nThe 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:\n\n\u003e 1. If _**r\u2019**_ is not an integer in the interval _**[1, n-1]**_, then reject the signature.\n\u003e 2. If _**s\u2019**_ is not an integer in the interval _**[1, n-1]**_, then reject the signature.\n\nFor example, consider the following excerpt of the verify function from the [ecdsa-python implementation](https://github.com/starkbank/ecdsa-python/blob/v2.0.0/ellipticcurve/ecdsa.py#L34-L41).\n\n```python\ndef verify(cls, message, signature, publicKey, hashfunc=sha256):\n byteMessage = hashfunc(toBytes(message)).digest()\n numberMessage = numberFromByteString(byteMessage)\n curve = publicKey.curve\n r = signature.r\n s = signature.s\n inv = Math.inv(s, curve.N)\n u1 = Math.multiply(curve.G, n=(numberMessage * inv) % curve.N, N=curve.N, A=curve.A, P=curve.P)\n u2 = Math.multiply(publicKey.point, n=(r * inv) % curve.N, N=curve.N, A=curve.A, P=curve.P)\n add = Math.add(u1, u2, A=curve.A, P=curve.P)\n modX = add.x % curve.N\n return r == modX\n```\n\nIn 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.\n\n### Recommendation\nUsers 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.\n\n- ecdsa-python: v2.0.1\n- ecdsa-java: v1.0.1\n- ecdsa-dotnet: v1.3.2\n- ecdsa-elixir v1.0.1\n- ecdsa-node v1.1.3",
"id": "GHSA-xx36-6rv4-gj8r",
"modified": "2023-09-27T21:49:47Z",
"published": "2022-05-24T19:20:12Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2021-43568"
},
{
"type": "WEB",
"url": "https://github.com/starkbank/ecdsa-elixir/commit/4b960e26768bb698f449eb7686b5664936b70b61"
},
{
"type": "WEB",
"url": "https://github.com/starkbank/ecdsa-elixir/commit/a5168f6d9cfbe0a0a62d92e2e9b1a97235d90343"
},
{
"type": "PACKAGE",
"url": "https://github.com/starkbank/ecdsa-elixir"
},
{
"type": "WEB",
"url": "https://github.com/starkbank/ecdsa-elixir/releases/tag/v1.0.1"
},
{
"type": "WEB",
"url": "https://research.nccgroup.com/2021/11/08/technical-advisory-arbitrary-signature-forgery-in-stark-bank-ecdsa-libraries"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
],
"summary": "ecdsa-elixir fails to check signatures, vulnerable to message forging"
}
GHSA-XXX4-CX36-38R5
Vulnerability from github – Published: 2022-05-24 19:19 – Updated: 2022-05-24 19:19Lack of email address ownership verification in the CODEOWNERS feature in all versions of GitLab EE since version 11.3 allows an attacker to bypass CODEOWNERS Merge Request approval requirement under rare circumstances
{
"affected": [],
"aliases": [
"CVE-2021-39909"
],
"database_specific": {
"cwe_ids": [
"CWE-347"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2021-11-05T00:15:00Z",
"severity": "MODERATE"
},
"details": "Lack of email address ownership verification in the CODEOWNERS feature in all versions of GitLab EE since version 11.3 allows an attacker to bypass CODEOWNERS Merge Request approval requirement under rare circumstances",
"id": "GHSA-xxx4-cx36-38r5",
"modified": "2022-05-24T19:19:53Z",
"published": "2022-05-24T19:19:53Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2021-39909"
},
{
"type": "WEB",
"url": "https://hackerone.com/reports/1237750"
},
{
"type": "WEB",
"url": "https://gitlab.com/gitlab-org/cves/-/blob/master/2021/CVE-2021-39909.json"
},
{
"type": "WEB",
"url": "https://gitlab.com/gitlab-org/gitlab/-/issues/335191"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N",
"type": "CVSS_V3"
}
]
}
No mitigation information available for this CWE.
CAPEC-463: Padding Oracle Crypto Attack
An adversary is able to efficiently decrypt data without knowing the decryption key if a target system leaks data on whether or not a padding error happened while decrypting the ciphertext. A target system that leaks this type of information becomes the padding oracle and an adversary is able to make use of that oracle to efficiently decrypt data without knowing the decryption key by issuing on average 128*b calls to the padding oracle (where b is the number of bytes in the ciphertext block). In addition to performing decryption, an adversary is also able to produce valid ciphertexts (i.e., perform encryption) by using the padding oracle, all without knowing the encryption key.
CAPEC-475: Signature Spoofing by Improper Validation
An adversary exploits a cryptographic weakness in the signature verification algorithm implementation to generate a valid signature without knowing the key.