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
AZL (1)
BELL (1)
CGA (6)
DEBIAN (1)
ECHO (1)
JLSEC (1)
MGASA (1)
OESA (3)
openSUSE (2)
RHSA (1)
ROOT (5)
SUSE (9)
UBUNTU (1)
Related
openSUSE (2)
SUSE (9)
Published
2026-07-24T16:45:24Z
Modified
2026-09-14T18:27:00Z
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 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.

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 
{
    "cpe":  "cpe:2.3:a:libssh2:libssh2:*:*:*:*:*:*:*:*",
    "extracted_events":  [
        {
            "introduced":  "0"
        },
        {
            "last_affected":  "1.11.1"
        }
    ],
    "source":  [
        "CPE_RANGE",
        "REFERENCES"
    ]
}

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 
[
    {
        "deprecated":  false,
        "digest":  {
            "function_hash":  "194798789246794431973226330957313786150",
            "length":  3574
        },
        "id":  "CVE-2026-66035-2a4095ef",
        "signature_type":  "Function",
        "signature_version":  "v1",
        "source":  "https://github.com/libssh2/libssh2/commit/42e33d81577ed4b95d4b4f6f845e5ee8efe5eeb4",
        "target":  {
            "file":  "src/transport.c",
            "function":  "transport_fullpacket"
        }
    },
    {
        "deprecated":  false,
        "digest":  {
            "line_hashes":  [
                "134169043152947898383512518039555862257",
                "104460753797033781775243388102015553353",
                "252879134917780202298535148269796609869",
                "132377937468879972229428824267623819060",
                "84558251560958915091751822719033683389",
                "283849024653323403509245380020001618044",
                "102304749765356114626298989055981403620"
            ],
            "threshold":  0.9
        },
        "id":  "CVE-2026-66035-64b57de0",
        "signature_type":  "Line",
        "signature_version":  "v1",
        "source":  "https://github.com/libssh2/libssh2/commit/42e33d81577ed4b95d4b4f6f845e5ee8efe5eeb4",
        "target":  {
            "file":  "src/transport.c"
        }
    }
]
vanir_signatures_modified 
"2026-08-12T16:09:59Z"