CVE-2026-66033

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Source
https://cve.org/CVERecord?id=CVE-2026-66033
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-66033.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2026-66033
Downstream
Related
Published
2026-07-24T16:35:28.607Z
Modified
2026-08-12T18:48:07.749966168Z
Severity
  • 8.7 (High) CVSS_V4 - CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N CVSS Calculator
Summary
libssh2 Integer Underflow DoS via AES-GCM Cipher Negotiation
Details

libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow vulnerability in the ssh2ciphercrypt() function in src/openssl.c that allows a malicious SSH server to crash any connecting client by negotiating AES-GCM ciphers during handshake. Attackers can exploit the underflow in the expression computing blocksize minus aadlen minus authentication tag length to trigger an out-of-bounds read and a memcpy call with a near-SIZE_MAX length argument, causing immediate process crash before any authentication occurs.

Database specific 
{
    "cna_assigner": "VulnCheck",
    "cwe_ids": [
        "CWE-125",
        "CWE-191"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/66xxx/CVE-2026-66033.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
a2ed82d40964bbc0d64cd717aa0a5a892117d2e6
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-2026-66033.json"
vanir_signatures 
[
    {
        "target": {
            "file": "src/openssl.c"
        },
        "deprecated": false,
        "source": "https://github.com/libssh2/libssh2/commit/a2ed82d40964bbc0d64cd717aa0a5a892117d2e6",
        "id": "CVE-2026-66033-89f09c5e",
        "signature_version": "v1",
        "digest": {
            "threshold": 0.9,
            "line_hashes": [
                "46633703602793041808516286579933556623",
                "279562781493981400548354506450174966742",
                "258491700871900350601374492589103506149",
                "235345207691640829178811662733441267462",
                "283781903113671097521482788622692922695",
                "208608583349629759841085481553437954960",
                "46721559972552605241860937490957983536"
            ]
        },
        "signature_type": "Line"
    },
    {
        "target": {
            "function": "ssh2_cipher_crypt",
            "file": "src/openssl.c"
        },
        "deprecated": false,
        "source": "https://github.com/libssh2/libssh2/commit/a2ed82d40964bbc0d64cd717aa0a5a892117d2e6",
        "id": "CVE-2026-66033-bb286c20",
        "signature_version": "v1",
        "digest": {
            "length": 1781.0,
            "function_hash": "284423643486394263830813353865833030823"
        },
        "signature_type": "Function"
    }
]
vanir_signatures_modified 
"2026-08-12T16:41:43Z"