CVE-2026-55199

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Source
https://cve.org/CVERecord?id=CVE-2026-55199
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-55199.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2026-55199
Downstream
Related
Published
2026-06-17T18:44:18Z
Modified
2026-08-26T18:27:58Z
Severity
  • 8.2 (High) CVSS_V4 - CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N CVSS Calculator
Summary
libssh2 - Pre-Authentication DoS via SSH_MSG_EXT_INFO Handler
Details

libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service vulnerability in the SSH_MSG_EXT_INFO handler in src/packet.c that allows a malicious SSH server to cause a client CPU exhaustion loop by sending a crafted extension count value. A malicious server can set nr_extensions to 0xFFFFFFFF during key exchange, causing the client to spin in a tight CPU loop for over 60 seconds because return values from _libssh2_get_string() are unchecked and the session timeout does not apply to CPU-bound loops.

Database specific 
{
    "cna_assigner": "VulnCheck",
    "cwe_ids": [
        "CWE-835"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55199.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
17626857d20b3c9a1addfa45979dadcee1cd84a4
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-2026-55199.json"
vanir_signatures 
[
    {
        "deprecated": false,
        "digest": {
            "line_hashes": [
                "67122845657668344552371962070822576711",
                "149606929713965925426466961564282333041",
                "192278621762336052757313921640537879588",
                "138666448627037029192090976022784337754",
                "333614903892572360934878653345642136656"
            ],
            "threshold": 0.9
        },
        "id": "CVE-2026-55199-00f7cd61",
        "signature_type": "Line",
        "signature_version": "v1",
        "source": "https://github.com/libssh2/libssh2/commit/17626857d20b3c9a1addfa45979dadcee1cd84a4",
        "target": {
            "file": "src/packet.c"
        }
    },
    {
        "deprecated": false,
        "digest": {
            "function_hash": "202695723005422450388970061283937754254",
            "length": 16686
        },
        "id": "CVE-2026-55199-da3d9784",
        "signature_type": "Function",
        "signature_version": "v1",
        "source": "https://github.com/libssh2/libssh2/commit/17626857d20b3c9a1addfa45979dadcee1cd84a4",
        "target": {
            "file": "src/packet.c",
            "function": "_libssh2_packet_add"
        }
    }
]
vanir_signatures_modified 
"2026-08-12T16:09:46Z"