BREW-LIBSSH2-CVE-2026-66035 (CVE-2026-66035)
Vulnerability from osv_homebrew – Published: 2026-08-05 16:54 – Updated: 2026-08-05 16:54 – Source websitelibssh2 through 1.11.1, fixed in commit 42e33d8, contains a pre-authentication heap buffer overflow vulnerability that allows a malicious SSH server to corrupt heap metadata in any connecting client by sending a packet with a packet_length smaller than the cipher's block size during Encrypt-then-MAC cipher negotiation. In the fullpacket() function in src/transport.c, the ETM path allocates a buffer of packet_length bytes but copies blocksize minus one bytes via memcpy, causing an overflow that on 32-bit glibc writes attacker-controlled bytes into an adjacent chunk's SIZE field, enabling tcache bin confusion, overlapping live objects, and function pointer overwrite during the session handshake before authentication.
{
"affected": [
{
"ecosystem_specific": {
"fix": "patch",
"patches": [
{
"file": "Patches/libssh2/CVE-2026-66035.patch",
"type": "backport"
}
]
},
"package": {
"ecosystem": "Homebrew",
"name": "libssh2",
"purl": "pkg:brew/libssh2"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.11.1_4"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"source": "generated"
},
"details": "libssh2 through 1.11.1, fixed in commit 42e33d8, contains a pre-authentication heap buffer overflow vulnerability that allows a malicious SSH server to corrupt heap metadata in any connecting client by sending a packet with a packet_length smaller than the cipher\u0027s block size during Encrypt-then-MAC cipher negotiation. In the fullpacket() function in src/transport.c, the ETM path allocates a buffer of packet_length bytes but copies blocksize minus one bytes via memcpy, causing an overflow that on 32-bit glibc writes attacker-controlled bytes into an adjacent chunk\u0027s SIZE field, enabling tcache bin confusion, overlapping live objects, and function pointer overwrite during the session handshake before authentication.",
"id": "BREW-libssh2-CVE-2026-66035",
"modified": "2026-08-05T16:54:10Z",
"published": "2026-08-05T16:54:10Z",
"references": [
{
"type": "ADVISORY",
"url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/66xxx/CVE-2026-66035.json"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-66035"
},
{
"type": "ADVISORY",
"url": "https://www.vulncheck.com/advisories/libssh2-heap-buffer-overflow-via-etm-cipher-negotiation"
},
{
"type": "FIX",
"url": "https://github.com/libssh2/libssh2/commit/42e33d81577ed4b95d4b4f6f845e5ee8efe5eeb4"
},
{
"type": "FIX",
"url": "https://github.com/libssh2/libssh2/pull/2198"
},
{
"type": "PACKAGE",
"url": "https://github.com/libssh2/libssh2"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": "libssh2 Heap Buffer Overflow via ETM Cipher Negotiation",
"upstream": [
"CVE-2026-66035"
]
}
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| Author | Source | Type | Date | Other |
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Nomenclature
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Sightings and recorded dates, grouped by day · UTC
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