Vulnerability-Lookup

CVE-2026-55199 (GCVE-0-2026-55199)

Vulnerability from cvelistv5 – Published: 2026-06-17 18:44 – Updated: 2026-07-14 21:33 X_Open Source

Title

libssh2 - Pre-Authentication DoS via SSH_MSG_EXT_INFO Handler

Summary

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.

Severity

8.2 (High)


                        
                          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

5.9 (Medium)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-06-18 15:31 UTC

CWE

CWE-835 - Loop with Unreachable Exit Condition ('Infinite Loop')

Assigner

VulnCheck mitre root

References

3 references

URL	Tags
https://github.com/libssh2/libssh2/pull/1864	issue-tracking
https://github.com/libssh2/libssh2/commit/1762685…	patch
https://www.vulncheck.com/advisories/libssh2-pre-…	third-party-advisory

Impacted products

1 product

Vendor	Product	Version	CPE status
libssh2	libssh2	Affected: 0 , ≤ 1.11.1 (semver) Unaffected: 17626857d20b3c9a1addfa45979dadcee1cd84a4 (git) cpe:2.3:a:libssh2:libssh2::::::::

Date Public

2026-04-15 00:00

Credits

Tristan Madani (@TristanInSec)

Show details on NVD website

JSON

To clipboard

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CERTFR-2026-AVI-0841

Vulnerability from certfr_avis - Published: 2026-07-07 - Updated: 2026-07-07

De multiples vulnérabilités ont été découvertes dans Microsoft Azure Linux. Elles permettent à un attaquant de provoquer un problème de sécurité non spécifié par l'éditeur.

Solutions

Se référer au bulletin de sécurité de l'éditeur pour l'obtention des correctifs (cf. section Documentation).

Impacted products

Vendor	Product	Description
Microsoft	Azure Linux	azl3 dhcpcd 10.0.8-2 versions antérieures à 10.0.8-4
Microsoft	Azure Linux	azl3 runc 1.3.3-2 versions antérieures à 1.3.6-1
Microsoft	Azure Linux	azl3 util-linux 2.40.2-4 versions antérieures à 2.40.2-5
Microsoft	Azure Linux	azl3 perl-Bytes-Random-Secure 0.29-21 versions antérieures à 0.29-22
Microsoft	Azure Linux	azl3 libssh2 1.11.1-3 versions antérieures à 1.11.1-4
Microsoft	Azure Linux	azl3 qemu 9.1.0-9 versions antérieures à 9.1.0-10
Microsoft	Azure Linux	azl3 tmux 3.4-1 versions antérieures à 3.4-2
Microsoft	Azure Linux	azl3 nmap 7.95-3 versions antérieures à 7.95-4

References

Title

Publication Time

FKIE_CVE-2026-55199

Vulnerability from fkie_nvd - Published: 2026-06-17 20:17 - Updated: 2026-07-14 22:17

Severity

5.9 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Summary

References

URL	Tags
disclosure@vulncheck.com	https://github.com/libssh2/libssh2/commit/17626857d20b3c9a1addfa45979dadcee1cd84a4	Patch
disclosure@vulncheck.com	https://github.com/libssh2/libssh2/pull/1864	Patch
disclosure@vulncheck.com	https://www.vulncheck.com/advisories/libssh2-pre-authentication-dos-via-ssh-msg-ext-info-handler	Third Party Advisory

Impacted products

	Vendor	Product	Version
	libssh2	libssh2	*

JSON

To clipboard

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              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "17626857d20b3c9a1addfa45979dadcee1cd84a4",
              "versionType": "git"
            }
          ]
        }
      ],
      "source": "disclosure@vulncheck.com"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:libssh2:libssh2:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "00D62356-F677-41CF-AC66-2871AD2112BA",
              "versionEndIncluding": "1.11.1",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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."
    }
  ],
  "id": "CVE-2026-55199",
  "lastModified": "2026-07-14T22:17:17.043",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 5.9,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 2.2,
        "impactScore": 3.6,
        "source": "disclosure@vulncheck.com",
        "type": "Secondary"
      },
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ],
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "PRESENT",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 8.2,
          "baseSeverity": "HIGH",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "NONE",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "userInteraction": "NONE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
          "version": "4.0",
          "vulnAvailabilityImpact": "HIGH",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "NONE",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "disclosure@vulncheck.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-55199",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-06-18T15:31:38.712448Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-06-17T20:17:28.520",
  "references": [
    {
      "source": "disclosure@vulncheck.com",
      "tags": [
        "Patch"
      ],
      "url": "https://github.com/libssh2/libssh2/commit/17626857d20b3c9a1addfa45979dadcee1cd84a4"
    },
    {
      "source": "disclosure@vulncheck.com",
      "tags": [
        "Patch"
      ],
      "url": "https://github.com/libssh2/libssh2/pull/1864"
    },
    {
      "source": "disclosure@vulncheck.com",
      "tags": [
        "Third Party Advisory"
      ],
      "url": "https://www.vulncheck.com/advisories/libssh2-pre-authentication-dos-via-ssh-msg-ext-info-handler"
    }
  ],
  "sourceIdentifier": "disclosure@vulncheck.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-835"
        }
      ],
      "source": "disclosure@vulncheck.com",
      "type": "Secondary"
    }
  ]
}

GHSA-3CFQ-4XX4-RMPG

Vulnerability from github – Published: 2026-06-17 21:34 – Updated: 2026-06-17 21:34

Details

Severity

5.9 (Medium)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

8.2 (High)


                  
                    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

Show details on source website

JSON

To clipboard

{
  "affected": [],
  "aliases": [
    "CVE-2026-55199"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-835"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-06-17T20:17:28Z",
    "severity": "HIGH"
  },
  "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.",
  "id": "GHSA-3cfq-4xx4-rmpg",
  "modified": "2026-06-17T21:34:39Z",
  "published": "2026-06-17T21:34:39Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-55199"
    },
    {
      "type": "WEB",
      "url": "https://github.com/libssh2/libssh2/pull/1864"
    },
    {
      "type": "WEB",
      "url": "https://github.com/libssh2/libssh2/commit/17626857d20b3c9a1addfa45979dadcee1cd84a4"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/libssh2-pre-authentication-dos-via-ssh-msg-ext-info-handler"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ]
}

MSRC_CVE-2026-55199

Vulnerability from csaf_microsoft - Published: 2026-06-02 00:00 - Updated: 2026-07-06 14:42

Summary

libssh2 - Pre-Authentication DoS via SSH_MSG_EXT_INFO Handler

Scope

1 vulnerability in this advisory, including CVE-2026-55199.

CVE-2026-55199

5.9 (Medium)


                
                  CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Fixed: 2 products Known affected: 4 products Known not affected: 1 product

https://learn.microsoft.com/en-us/azure/azure-linux/tutoria…

Open the full advisory

NCSC-2026-0210

Vulnerability from csaf_ncscnl - Published: 2026-06-23 09:53 - Updated: 2026-06-24 09:01

Summary

Kwetsbaarheden verholpen in libssh2 door libssh

Scope

2 vulnerabilities in this advisory, including CVE-2026-55199.

CVE-2026-55199

libssh2 versions through 1.11.1 contain a pre-authentication denial of service vulnerability in the SSH_MSG_EXT_INFO handler that allows a malicious SSH server to cause client CPU exhaustion via a crafted extension count, fixed in commit 1762685.

5.9 (Medium)


                
                  CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Known affected: 2 products

Open the full advisory

RHSA-2026:29950

Vulnerability from csaf_redhat - Published: 2026-06-25 13:02 - Updated: 2026-09-10 08:00

Summary

Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update

Severity

Moderate

Scope

2 vulnerabilities in this advisory, including CVE-2026-55199.

CVE-2026-55199

A vulnerability in libssh2 allows a malicious SSH server to freeze connected clients during the handshake process. By sending a malformed packet, the server triggers a loop that exhausts the client's CPU, resulting in a denial of service.

5.9 (Medium)


                
                  CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Fixed: 4 products

https://access.redhat.com/errata/RHSA-2026:29950

Open the full advisory

SUSE-SU-2026:22284-1

Vulnerability from csaf_suse - Published: 2026-06-25 11:50 - Updated: 2026-06-25 11:50

Summary

Security update for libssh2_org

Severity

Important

Scope

2 vulnerabilities in this advisory, including CVE-2026-55199.

CVE-2026-55199

5.9 (Medium)


                
                  CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Recommended: 4 products

Open the full advisory

SUSE-SU-2026:22364-1

Vulnerability from csaf_suse - Published: 2026-06-25 11:50 - Updated: 2026-06-25 11:50

Summary

Security update for libssh2_org

Severity

Important

Scope

2 vulnerabilities in this advisory, including CVE-2026-55199.

CVE-2026-55199

5.9 (Medium)


                
                  CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Recommended: 16 products

Open the full advisory

SUSE-SU-2026:22438-1

Vulnerability from csaf_suse - Published: 2026-07-01 09:39 - Updated: 2026-07-01 09:39

Summary

Security update for libssh2_org

Severity

Moderate

Scope

1 vulnerability in this advisory, including CVE-2026-55199.

CVE-2026-55199

5.9 (Medium)


                
                  CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Recommended: 3 products

Open the full advisory

SUSE-SU-2026:3525-1

Vulnerability from csaf_suse - Published: 2026-08-07 13:08 - Updated: 2026-08-07 13:08

Summary

Security update for libssh2_org

Severity

Important

Scope

9 vulnerabilities in this advisory, including CVE-2026-55199.

CVE-2026-55199

5.9 (Medium)


                
                  CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Recommended: 23 products

Open the full advisory

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

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CVE-2026-55199 (GCVE-0-2026-55199)

Solutions

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Sightings

Nomenclature

Related by attack behaviour