GHSA-6GVQ-JCMP-8959
Vulnerability from github – Published: 2025-12-16 00:43 – Updated: 2025-12-20 02:32
VLAI?
Summary
ALTCHA Proof-of-Work Vulnerable to Challenge Splicing and Replay
Details
Impact
A cryptographic semantic binding flaw in ALTCHA libraries allows challenge payload splicing, which may enable replay attacks. The HMAC signature does not unambiguously bind challenge parameters to the nonce, allowing an attacker to reinterpret a valid proof-of-work submission with a modified expiration value. This may allow previously solved challenges to be reused beyond their intended lifetime, depending on server-side replay handling and deployment assumptions.
The vulnerability primarily impacts abuse-prevention mechanisms such as rate limiting and bot mitigation. It does not directly affect data confidentiality or integrity.
Patches
This issue has been addressed by enforcing explicit semantic separation between challenge parameters and the nonce during HMAC computation.
Users are advised to upgrade to patched versions.
Workarounds
As a mitigation, implementations may append a delimiter to the end of the salt value prior to HMAC computation (for example, <salt>?expires=<time>&). This prevents ambiguity between parameters and the nonce and is backward-compatible with existing implementations, as the delimiter is treated as a standard URL parameter separator.
Severity ?
6.5 (Medium)
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "altcha-lib"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.4.1"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Packagist",
"name": "altcha-org/altcha"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.3.1"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Go",
"name": "github.com/altcha-org/altcha-lib-go"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.0.0"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Maven",
"name": "org.altcha:altcha"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.3.0"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "RubyGems",
"name": "altcha"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.0.0"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "PyPI",
"name": "altcha"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.0.0"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Hex",
"name": "altcha"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.0.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2025-68113"
],
"database_specific": {
"cwe_ids": [
"CWE-115",
"CWE-347"
],
"github_reviewed": true,
"github_reviewed_at": "2025-12-16T00:43:52Z",
"nvd_published_at": "2025-12-16T01:15:53Z",
"severity": "MODERATE"
},
"details": "### Impact\n\nA cryptographic semantic binding flaw in ALTCHA libraries allows challenge payload splicing, which may enable replay attacks. The HMAC signature does not unambiguously bind challenge parameters to the nonce, allowing an attacker to reinterpret a valid proof-of-work submission with a modified expiration value. This may allow previously solved challenges to be reused beyond their intended lifetime, depending on server-side replay handling and deployment assumptions.\n\nThe vulnerability primarily impacts abuse-prevention mechanisms such as rate limiting and bot mitigation. It does not directly affect data confidentiality or integrity. \n\n### Patches\n\nThis issue has been addressed by enforcing explicit semantic separation between challenge parameters and the nonce during HMAC computation.\n\nUsers are advised to upgrade to patched versions.\n\n### Workarounds\n\nAs a mitigation, implementations may append a delimiter to the end of the `salt` value prior to HMAC computation (for example, `\u003csalt\u003e?expires=\u003ctime\u003e\u0026`). This prevents ambiguity between parameters and the nonce and is backward-compatible with existing implementations, as the delimiter is treated as a standard URL parameter separator.",
"id": "GHSA-6gvq-jcmp-8959",
"modified": "2025-12-20T02:32:17Z",
"published": "2025-12-16T00:43:52Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/altcha-org/altcha-lib/security/advisories/GHSA-6gvq-jcmp-8959"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-68113"
},
{
"type": "WEB",
"url": "https://github.com/altcha-org/altcha-lib-ex/commit/09b2bad466ad0338a5b24245380950ea9918333e"
},
{
"type": "WEB",
"url": "https://github.com/altcha-org/altcha-lib-go/commit/4a5610745ef79895a67bac858b2e4f291c2614b8"
},
{
"type": "WEB",
"url": "https://github.com/altcha-org/altcha-lib-java/commit/69277651fdd6418ae10bf3a088901506f9c62114"
},
{
"type": "WEB",
"url": "https://github.com/altcha-org/altcha-lib-php/commit/9e9e70c864a9db960d071c77c778be0c9ff1a4d0"
},
{
"type": "WEB",
"url": "https://github.com/altcha-org/altcha-lib-rb/commit/4fd7b64cbbfc713f3ca4e066c2dd466e3b8d359b"
},
{
"type": "WEB",
"url": "https://github.com/altcha-org/altcha-lib/commit/cb95d83a8d08e273b6be15e48988e7eaf60d5c08"
},
{
"type": "PACKAGE",
"url": "https://github.com/altcha-org/altcha-lib"
},
{
"type": "WEB",
"url": "https://github.com/altcha-org/altcha-lib-java/releases/tag/v1.3.0"
},
{
"type": "WEB",
"url": "https://github.com/altcha-org/altcha-lib-php/releases/tag/v1.3.1"
},
{
"type": "WEB",
"url": "https://github.com/altcha-org/altcha-lib/releases/tag/1.4.1"
},
{
"type": "WEB",
"url": "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/altcha/CVE-2025-68113.yml"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L",
"type": "CVSS_V3"
}
],
"summary": "ALTCHA Proof-of-Work Vulnerable to Challenge Splicing and Replay"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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