{"cve":"CVE-2025-39703","nvd":{"published":"2025-09-05T18:15:47.417","modified":"2026-10-19T21:10:00.160","status":"Modified","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet, hsr: reject HSR frame if skb can't hold tag\n\nReceiving HSR frame with insufficient space to hold HSR tag in the skb\ncan result in a crash (kernel BUG):\n\n[   45.390915] skbuff: skb_under_panic: text:ffffffff86f32cac len:26 put:14 head:ffff888042418000 data:ffff888042417ff4 tail:0xe end:0x180 dev:bridge_slave_1\n[   45.392559] ------------[ cut here ]------------\n[   45.392912] kernel BUG at net/core/skbuff.c:211!\n[   45.393276] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI\n[   45.393809] CPU: 1 UID: 0 PID: 2496 Comm: reproducer Not tainted 6.15.0 #12 PREEMPT(undef)\n[   45.394433] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014\n[   45.395273] RIP: 0010:skb_panic+0x15b/0x1d0\n\n<snip registers, remove unreliable trace>\n\n[   45.402911] Call Trace:\n[   45.403105]  <IRQ>\n[   45.404470]  skb_push+0xcd/0xf0\n[   45.404726]  br_dev_queue_push_xmit+0x7c/0x6c0\n[   45.406513]  br_forward_finish+0x128/0x260\n[   45.408483]  __br_forward+0x42d/0x590\n[   45.409464]  maybe_deliver+0x2eb/0x420\n[   45.409763]  br_flood+0x174/0x4a0\n[   45.410030]  br_handle_frame_finish+0xc7c/0x1bc0\n[   45.411618]  br_handle_frame+0xac3/0x1230\n[   45.413674]  __netif_receive_skb_core.constprop.0+0x808/0x3df0\n[   45.422966]  __netif_receive_skb_one_core+0xb4/0x1f0\n[   45.424478]  __netif_receive_skb+0x22/0x170\n[   45.424806]  process_backlog+0x242/0x6d0\n[   45.425116]  __napi_poll+0xbb/0x630\n[   45.425394]  net_rx_action+0x4d1/0xcc0\n[   45.427613]  handle_softirqs+0x1a4/0x580\n[   45.427926]  do_softirq+0x74/0x90\n[   45.428196]  </IRQ>\n\nThis issue was found by syzkaller.\n\nThe panic happens in br_dev_queue_push_xmit() once it receives a\ncorrupted skb with ETH header already pushed in linear data. When it\nattempts the skb_push() call, there's not enough headroom and\nskb_push() panics.\n\nThe corrupted skb is put on the queue by HSR layer, which makes a\nsequence of unintended transformations when it receives a specific\ncorrupted HSR frame (with incomplete TAG).\n\nFix it by dropping and consuming frames that are not long enough to\ncontain both ethernet and hsr headers.\n\nAlternative fix would be to check for enough headroom before skb_push()\nin br_dev_queue_push_xmit().\n\nIn the reproducer, this is injected via AF_PACKET, but I don't easily\nsee why it couldn't be sent over the wire from adjacent network.\n\nFurther Details:\n\nIn the reproducer, the following network interface chain is set up:\n\n┌────────────────┐   ┌────────────────┐\n│ veth0_to_hsr   ├───┤  hsr_slave0    ┼───┐\n└────────────────┘   └────────────────┘   │\n                                          │ ┌──────┐\n                                          ├─┤ hsr0 ├───┐\n                                          │ └──────┘   │\n┌────────────────┐   ┌────────────────┐   │            │┌────────┐\n│ veth1_to_hsr   ┼───┤  hsr_slave1    ├───┘            └┤        │\n└────────────────┘   └────────────────┘                ┌┼ bridge │\n                                                       ││        │\n                                                       │└────────┘\n                                                       │\n                                        ┌───────┐      │\n                                        │  ...  ├──────┘\n                                        └───────┘\n\nTo trigger the events leading up to crash, reproducer sends a corrupted\nHSR fr\n---truncated---","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":5.5},"cwes":["CWE-476"],"references":["https://git.kernel.org/stable/c/3ae272ab523dd6bdc26e879027ed79feac9dd1b3","https://git.kernel.org/stable/c/61009439e4bd8d74e705ee15940760321be91d8a","https://git.kernel.org/stable/c/7af76e9d18a9fd6f8611b3313c86c190f9b6a5a7","https://git.kernel.org/stable/c/8d9bc4a375a1ba05f7dfa0407de8e510ab9bd14d","https://git.kernel.org/stable/c/acd69b597bd3f76d3b3d322b84082226c00eeaa4"],"products":["debian:debian_linux","linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-21T03:43:09.190223697+00:00"},"epss":{"cve":"CVE-2025-39703","score":0.00376,"percentile":0.31252,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}