{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-98401", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-25T10:25:14.346Z", "datePublished": "2026-10-14T13:26:01.712Z", "dateUpdated": "2026-10-24T14:08:43.092Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-24T14:08:43.092Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: iptunnel: fix stale transport header during tunnel decapsulation\n\nSyzbot reported a crash in qdisc_pkt_len_segs_init() caused by a stale\ntransport_header offset after tunnel decapsulation.\n\nBUG: unable to handle page fault for address: ffffed102091a42e\nOops: Oops: 0000 [#1] SMP KASAN NOPTI\nCPU: 0 UID: 0 PID: 340 Comm: qdisc_uaf_repro Not tainted 7.2.0-rc4-00061-g248951ddc14d #256 PREEMPT(full)\nHardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014\nRIP: 0010:__asan_load2\n\nqdisc_pkt_len_segs_init (net/core/dev.c:4145)\n__dev_queue_xmit (net/core/dev.c:4787)\nbr_dev_queue_push_xmit (net/bridge/br_forward.c:53)\nbr_handle_frame_finish (net/bridge/br_input.c:229)\nbr_handle_frame (net/bridge/br_input.c:315)\n__netif_receive_skb_core.constprop.0 (net/core/dev.c:6099)\n__netif_receive_skb_list_core (net/core/dev.c:6287)\nnetif_receive_skb_list_internal (net/core/dev.c:6445)\nnapi_complete_done (net/core/dev.c:6813)\ngro_cell_poll (net/core/gro_cells.c:74)\n__napi_poll (net/core/dev.c:7735)\nnet_rx_action (net/core/dev.c:7798 net/core/dev.c:7955)\nhandle_softirqs (kernel/softirq.c:622)\ndo_softirq (kernel/softirq.c:523 kernel/softirq.c:510 )\n__local_bh_enable_ip (kernel/softirq.c:450)\ntun_get_user (drivers/net/tun.c:1986 (discriminator 1))\ntun_chr_write_iter (drivers/net/tun.c:2032)\n\nThe issue is completely latent until qdisc read transport header in\ncommit 7fb4c1967011 (\"net: pull headers in qdisc_pkt_len_segs_init()\").\nThe crash requires four conditions to line up:\n\n1. The incoming packet is encapsulated and carries GSO metadata. The outer\n transport header offset is stored in skb->transport_header while the\n packet is still in the outer tunnel context.\n2. The tunnel receiver strips the outer headers. skb->data is advanced to\n the inner frame, but skb->transport_header is left pointing to the\n now-removed outer L4 header, so it becomes a negative offset relative to\n the new data.\n3. The inner frame is not delivered to the local IP stack. Instead, it\n is forwarded at L2 by a bridge or HSR, so ip_rcv_core() never runs and\n the transport header is not reset to the inner L4 offset.\n4. The forwarding path calls __dev_queue_xmit(), which enters\n qdisc_pkt_len_segs_init(). That function computes the GSO header length\n from skb_transport_offset(skb). Because the offset is negative, the\n unsigned cast overflows and pskb_may_pull(skb, hdr_len +\n sizeof(struct tcphdr)) reads past the end of the skb, triggering a\n KASAN fault or page fault.\n\nThe issue specifically requires GSO packets (shinfo->gso_size != 0), which\nare processed/aggregated through gro_cells. Fix this by clearing\ntransport_header to the ~0U sentinel in gro_cell for all tunnnel driver.\nGTP does not support GRO/GSO, drop the evil GSO packets in GTP directly." } ], "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 - An unauthenticated peer can send IPv4/IPv6 GRE packets carrying inner TCP frames; gre_gro_receive() creates the GSO skb, and gre_rcv() through ip6_tnl_rcv() reaches the patched gro_cells_receive() before bridge forwarding invokes qdisc_pkt_len_segs_init().\nAC:L - On a bridged GRETAP endpoint, the attacker sends same-flow GRE-encapsulated TCP segments to induce GRO and chooses a nonlocal inner destination so br_handle_frame_finish() forwards them. These packet conditions are attacker-controlled and require no race.\nPR:N - ip6_input_finish() dispatches protocol 47 to gre_rcv(), where ip6gre_tunnel_lookup() selects the configured tunnel without authenticating the sender or checking task credentials. No target-system privilege is required once the GRETAP endpoint is running.\nUI:N - The received GRE stream automatically traverses GRO, gre_rcv(), gro_cells_receive(), and bridge egress; no victim must open data, approve a request, or perform another action.\nS:U - qdisc_pkt_len_segs_init() dereferences the invalid skb header pointer inside the host kernel's receive and forwarding paths. The resulting fault does not cross a VM, IOMMU, or other security-authority boundary.\nC:N - After basic GRE decapsulation and bridge Ethernet-header restoration, the stale transport offset is -4; unsigned wrap makes __tcp_hdrlen() perform a two-byte invalid read, but the value is only used for header-length and drop accounting and is never copied or returned to the peer.\nI:N - __tcp_hdrlen() only reads th->doff through the invalid pointer; subsequent code drops the skb or updates its qdisc length metadata. The code provides no write primitive or demonstrated modification of protected kernel or user data.\nA:H - The out-of-bounds th->doff load in qdisc_pkt_len_segs_init() can fault roughly 4 GiB beyond skb->data. The observed bridge-forwarding path produces a KASAN or page-fault Oops and can be triggered repeatedly with packet streams." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "drivers/net/gtp.c", "include/linux/skbuff.h", "net/core/gro_cells.c" ], "versions": [ { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "8c3d4dfcecf7670c1d752f1ae74b21b2af5feac1", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "e4a5b01e59f7102169762b8f566c8e052d05c0ff", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "3340b8565b85631cfeb0df049e8b46e3ef8bd7bd", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "28a57fb2c5df4deb42a06e52fd36c14b37aa0034", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "drivers/net/gtp.c", "include/linux/skbuff.h", "net/core/gro_cells.c" ], "versions": [ { "version": "2.6.12", "status": "affected" }, { "version": "0", "lessThan": "2.6.12", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.111", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.53", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2.7", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.3", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "6.12.111" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "6.18.53" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "7.2.7" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/8c3d4dfcecf7670c1d752f1ae74b21b2af5feac1" }, { "url": "https://git.kernel.org/stable/c/e4a5b01e59f7102169762b8f566c8e052d05c0ff" }, { "url": "https://git.kernel.org/stable/c/3340b8565b85631cfeb0df049e8b46e3ef8bd7bd" }, { "url": "https://git.kernel.org/stable/c/28a57fb2c5df4deb42a06e52fd36c14b37aa0034" } ], "title": "net: iptunnel: fix stale transport header during tunnel decapsulation", "x_generator": { "engine": "bippy-1.2.0" } } } }