CVE-2026-66035

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Source
https://cve.org/CVERecord?id=CVE-2026-66035
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-66035.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2026-66035
Downstream
Related
Published
2026-07-24T16:45:24.405Z
Modified
2026-08-12T18:48:15.092804203Z
Severity
  • 7.7 (High) CVSS_V4 - 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 CVSS Calculator
Summary
libssh2 Heap Buffer Overflow via ETM Cipher Negotiation
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 packetlength 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 packetlength 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.

Database specific 
{
    "cna_assigner": "VulnCheck",
    "cwe_ids": [
        "CWE-122"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/66xxx/CVE-2026-66035.json"
}
References

Affected packages

Git / github.com/libssh2/libssh2

Affected ranges

Type
GIT
Repo
https://github.com/libssh2/libssh2
Events
Introduced
0 Unknown introduced commit / All previous commits are affected
Fixed
42e33d81577ed4b95d4b4f6f845e5ee8efe5eeb4
Database specific
Show details 
{
    "extracted_events": [
        {
            "introduced": "0"
        },
        {
            "last_affected": "1.11.1"
        }
    ],
    "source": [
        "CPE_RANGE",
        "REFERENCES"
    ],
    "cpe": "cpe:2.3:a:libssh2:libssh2:*:*:*:*:*:*:*:*"
}

Affected versions

RELEASE.*
RELEASE.0.1
RELEASE.0.10
RELEASE.0.11
RELEASE.0.12
RELEASE.0.13
RELEASE.0.14
RELEASE.0.15
RELEASE.0.16
RELEASE.0.17
RELEASE.0.18
RELEASE.0.3
RELEASE.0.5
RELEASE.0.6
RELEASE.0.7
RELEASE.0.8
RELEASE.1.0
RELEASE.1.1
beforenb-0.*
beforenb-0.14
beforenb2-0.*
beforenb2-0.14
libssh2-1.*
libssh2-1.10.0
libssh2-1.11.0
libssh2-1.11.1
libssh2-1.2
libssh2-1.2.1
libssh2-1.2.3
libssh2-1.2.4
libssh2-1.2.5
libssh2-1.2.6
libssh2-1.2.7
libssh2-1.2.8
libssh2-1.2.9
libssh2-1.3.0
libssh2-1.4.0
libssh2-1.4.1
libssh2-1.4.2
libssh2-1.4.3
libssh2-1.5.0
libssh2-1.6.0
libssh2-1.7.0
libssh2-1.8.0
libssh2-1.9.0

Database specific

source 
"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-66035.json"
vanir_signatures 
[
    {
        "target": {
            "function": "transport_fullpacket",
            "file": "src/transport.c"
        },
        "deprecated": false,
        "source": "https://github.com/libssh2/libssh2/commit/42e33d81577ed4b95d4b4f6f845e5ee8efe5eeb4",
        "id": "CVE-2026-66035-2a4095ef",
        "signature_version": "v1",
        "digest": {
            "length": 3574.0,
            "function_hash": "194798789246794431973226330957313786150"
        },
        "signature_type": "Function"
    },
    {
        "digest": {
            "threshold": 0.9,
            "line_hashes": [
                "134169043152947898383512518039555862257",
                "104460753797033781775243388102015553353",
                "252879134917780202298535148269796609869",
                "132377937468879972229428824267623819060",
                "84558251560958915091751822719033683389",
                "283849024653323403509245380020001618044",
                "102304749765356114626298989055981403620"
            ]
        },
        "source": "https://github.com/libssh2/libssh2/commit/42e33d81577ed4b95d4b4f6f845e5ee8efe5eeb4",
        "deprecated": false,
        "id": "CVE-2026-66035-64b57de0",
        "signature_version": "v1",
        "signature_type": "Line",
        "target": {
            "file": "src/transport.c"
        }
    }
]
vanir_signatures_modified 
"2026-08-12T16:09:59Z"