{"id":"CVE-2026-43254","state":"PUBLISHED","title":"ovpn: tcp - fix packet extraction from stream","description":"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%.","publishedAt":"2026-05-06T11:28:43.871Z","updatedAt":"2026-08-05T12:26:54.790Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"11851cbd60ea1e5abbd97619d69845ead99303d6","status":"affected","lessThan":"0315bec883c67fa1413c61e504a28dc5bd02eb37","versionType":"git"},{"version":"11851cbd60ea1e5abbd97619d69845ead99303d6","status":"affected","lessThan":"7dba6cd7fb168d7615194a631c9c100c1c224131","versionType":"git"},{"version":"11851cbd60ea1e5abbd97619d69845ead99303d6","status":"affected","lessThan":"d4f687fbbce45b5e88438e89b5e26c0c15847992","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ovpn/tcp.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.16","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.16","versionType":"semver"},{"version":"6.18.16","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.6","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ovpn/tcp.c"]}],"references":["https://git.kernel.org/stable/c/0315bec883c67fa1413c61e504a28dc5bd02eb37","https://git.kernel.org/stable/c/7dba6cd7fb168d7615194a631c9c100c1c224131","https://git.kernel.org/stable/c/d4f687fbbce45b5e88438e89b5e26c0c15847992"],"weaknesses":[],"ingestedAt":"2026-10-29T20:11:57.932Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/43xxx/CVE-2026-43254.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-43254","state":"PUBLISHED","datePublished":"2026-05-06T11:28:43.871Z","dateUpdated":"2026-08-05T12:26:54.790Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-05-01T14:12:55.996Z"},"containers":{"cna":{"title":"ovpn: tcp - fix packet extraction from stream","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%."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"11851cbd60ea1e5abbd97619d69845ead99303d6","status":"affected","lessThan":"0315bec883c67fa1413c61e504a28dc5bd02eb37","versionType":"git"},{"version":"11851cbd60ea1e5abbd97619d69845ead99303d6","status":"affected","lessThan":"7dba6cd7fb168d7615194a631c9c100c1c224131","versionType":"git"},{"version":"11851cbd60ea1e5abbd97619d69845ead99303d6","status":"affected","lessThan":"d4f687fbbce45b5e88438e89b5e26c0c15847992","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ovpn/tcp.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.16","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.16","versionType":"semver"},{"version":"6.18.16","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.6","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ovpn/tcp.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/0315bec883c67fa1413c61e504a28dc5bd02eb37"},{"url":"https://git.kernel.org/stable/c/7dba6cd7fb168d7615194a631c9c100c1c224131"},{"url":"https://git.kernel.org/stable/c/d4f687fbbce45b5e88438e89b5e26c0c15847992"}],"metrics":[{"cvssV3_1":{"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"},"scenarios":[{"lang":"en","value":"AV:N - The vulnerable parser is reached by TCP stream data received from a remote OpenVPN peer over the network.\nAC:L - The attacker controls the TCP byte stream and OpenVPN length-prefixed records; no race or condition outside attacker control is required.\nPR:N - Local CAP_NET_ADMIN is needed only to configure the ovpn device and attach the socket, not to send the triggering network data once the service is exposed.\nUI:N - No victim user action is needed beyond the already-running OpenVPN TCP deployment.\nS:U - The impact remains within the kernel/OpenVPN networking security authority and does not cross a VM, sandbox, or hardware isolation boundary.\nC:N - The traced path leads to packet extraction/header-offset failure and drops, with no demonstrated kernel memory disclosure primitive.\nI:N - The bug corrupts skb parsing state/alignment but does not provide a demonstrated ability to modify kernel memory or protected data.\nA:H - A remote sender can repeatedly trigger packet drops in the ovpn TCP data path, and on strict-alignment systems the unaligned kernel accesses can severely disrupt or crash the data channel."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T12:26:54.790Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.16","versionEndExcluding":"6.18.16"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.16","versionEndExcluding":"6.19.6"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.16","versionEndExcluding":"7.0"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}