{"cve":"CVE-2025-39828","nvd":{"published":"2025-09-16T13:16:03.373","modified":"2026-10-19T21:10:00.160","status":"Modified","description":"In the Linux kernel, the following vulnerability has been resolved:\n\natm: atmtcp: Prevent arbitrary write in atmtcp_recv_control().\n\nsyzbot reported the splat below. [0]\n\nWhen atmtcp_v_open() or atmtcp_v_close() is called via connect()\nor close(), atmtcp_send_control() is called to send an in-kernel\nspecial message.\n\nThe message has ATMTCP_HDR_MAGIC in atmtcp_control.hdr.length.\nAlso, a pointer of struct atm_vcc is set to atmtcp_control.vcc.\n\nThe notable thing is struct atmtcp_control is uAPI but has a\nspace for an in-kernel pointer.\n\n  struct atmtcp_control {\n  \tstruct atmtcp_hdr hdr;\t/* must be first */\n  ...\n  \tatm_kptr_t vcc;\t\t/* both directions */\n  ...\n  } __ATM_API_ALIGN;\n\n  typedef struct { unsigned char _[8]; } __ATM_API_ALIGN atm_kptr_t;\n\nThe special message is processed in atmtcp_recv_control() called\nfrom atmtcp_c_send().\n\natmtcp_c_send() is vcc->dev->ops->send() and called from 2 paths:\n\n  1. .ndo_start_xmit() (vcc->send() == atm_send_aal0())\n  2. vcc_sendmsg()\n\nThe problem is sendmsg() does not validate the message length and\nuserspace can abuse atmtcp_recv_control() to overwrite any kptr\nby atmtcp_control.\n\nLet's add a new ->pre_send() hook to validate messages from sendmsg().\n\n[0]:\nOops: general protection fault, probably for non-canonical address 0xdffffc00200000ab: 0000 [#1] SMP KASAN PTI\nKASAN: probably user-memory-access in range [0x0000000100000558-0x000000010000055f]\nCPU: 0 UID: 0 PID: 5865 Comm: syz-executor331 Not tainted 6.17.0-rc1-syzkaller-00215-gbab3ce404553 #0 PREEMPT(full)\nHardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025\nRIP: 0010:atmtcp_recv_control drivers/atm/atmtcp.c:93 [inline]\nRIP: 0010:atmtcp_c_send+0x1da/0x950 drivers/atm/atmtcp.c:297\nCode: 4d 8d 75 1a 4c 89 f0 48 c1 e8 03 42 0f b6 04 20 84 c0 0f 85 15 06 00 00 41 0f b7 1e 4d 8d b7 60 05 00 00 4c 89 f0 48 c1 e8 03 <42> 0f b6 04 20 84 c0 0f 85 13 06 00 00 66 41 89 1e 4d 8d 75 1c 4c\nRSP: 0018:ffffc90003f5f810 EFLAGS: 00010203\nRAX: 00000000200000ab RBX: 0000000000000000 RCX: 0000000000000000\nRDX: ffff88802a510000 RSI: 00000000ffffffff RDI: ffff888030a6068c\nRBP: ffff88802699fb40 R08: ffff888030a606eb R09: 1ffff1100614c0dd\nR10: dffffc0000000000 R11: ffffffff8718fc40 R12: dffffc0000000000\nR13: ffff888030a60680 R14: 000000010000055f R15: 00000000ffffffff\nFS:  00007f8d7e9236c0(0000) GS:ffff888125c1c000(0000) knlGS:0000000000000000\nCS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\nCR2: 000000000045ad50 CR3: 0000000075bde000 CR4: 00000000003526f0\nCall Trace:\n <TASK>\n vcc_sendmsg+0xa10/0xc60 net/atm/common.c:645\n sock_sendmsg_nosec net/socket.c:714 [inline]\n __sock_sendmsg+0x219/0x270 net/socket.c:729\n ____sys_sendmsg+0x505/0x830 net/socket.c:2614\n ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668\n __sys_sendmsg net/socket.c:2700 [inline]\n __do_sys_sendmsg net/socket.c:2705 [inline]\n __se_sys_sendmsg net/socket.c:2703 [inline]\n __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703\n do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]\n do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94\n entry_SYSCALL_64_after_hwframe+0x77/0x7f\nRIP: 0033:0x7f8d7e96a4a9\nCode: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48\nRSP: 002b:00007f8d7e923198 EFLAGS: 00000246 ORIG_RAX: 000000000000002e\nRAX: ffffffffffffffda RBX: 00007f8d7e9f4308 RCX: 00007f8d7e96a4a9\nRDX: 0000000000000000 RSI: 0000200000000240 RDI: 0000000000000005\nRBP: 00007f8d7e9f4300 R08: 65732f636f72702f R09: 65732f636f72702f\nR10: 65732f636f72702f R11: 0000000000000246 R12: 00007f8d7e9c10ac\nR13: 00007f8d7e9231a0 R14: 0000200000000200 R15: 0000200000000250\n </TASK>\nModules linked in:","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","score":7.8},"cwes":[],"references":["https://git.kernel.org/stable/c/0a6a6d4fb333f7afe22e59ffed18511a7a98efc8","https://git.kernel.org/stable/c/33f9e6dc66b32202b95fc861e6b3ea4b0c185b0b","https://git.kernel.org/stable/c/3ab9f5ad9baefe6d3d4c37053cdfca2761001dfe","https://git.kernel.org/stable/c/3c80c230d6e3e6f63d43f4c3f0bb344e3e8b119b","https://git.kernel.org/stable/c/51872b26429077be611b0a1816e0e722278015c3"],"products":["debian:debian_linux","linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-21T03:43:09.190223697+00:00"},"epss":{"cve":"CVE-2025-39828","score":0.00172,"percentile":0.06527,"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."]}