{ "schemaVersion": 1, "attribution": [ { "source": "CISA Known Exploited Vulnerabilities", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog", "licence": "US government work" }, { "source": "GitHub Advisory Database", "url": "https://github.com/advisories", "licence": "CC BY 4.0" }, { "source": "Have I Been Pwned", "url": "https://haveibeenpwned.com/", "licence": "CC BY 4.0" }, { "source": "CVE Program (CVE records)", "url": "https://www.cve.org/Legal/TermsOfUse", "licence": "CVE Terms of Use", "notice": "Copyright © 1999-2026, The MITRE Corporation. CVE is a trademark and the CVE logo is a registered trademark of The MITRE Corporation.", "terms": "CVE Usage: MITRE hereby grants you a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, sublicense, and distribute Common Vulnerabilities and Exposures (CVE™). Any copy you make for such purposes is authorized provided that you reproduce MITRE's copyright designation and this license in any such copy." }, { "source": "FIRST EPSS", "url": "https://www.first.org/epss/", "licence": "free to use; FIRST requests attribution" } ], "record": { "id": "CVE-2023-53809", "sourceURL": "https://www.cve.org/CVERecord?id=CVE-2023-53809", "idYear": 2023, "status": "PUBLISHED", "publishedAt": "2025-12-09T00:01:07.120Z", "updatedAt": "2026-05-23T15:31:07.089Z", "importedAt": "2026-10-24T01:57:03.413Z", "snapshot": { "id": "cve_2026-10-24_midnight_baseline", "at": "2026-10-24T00:00:00.000Z", "source": "https://github.com/CVEProject/cvelistV5/releases/tag/cve_2026-10-24_0100Z" }, "facts": { "title": "l2tp: Avoid possible recursive deadlock in l2tp_tunnel_register()", "summary": "In the Linux kernel, the following vulnerability has been resolved:\n\nl2tp: Avoid possible recursive deadlock in l2tp_tunnel_register()\n\nWhen a file descriptor of pppol2tp socket is passed as file descriptor\nof UDP socket, a recursive deadlock occurs in l2tp_tunnel_register().\nThis situation is reproduced by the following program:\n\nint main(void)\n{\n\tint sock;\n\tstruct sockaddr_pppol2tp addr;\n\n\tsock = socket(AF_PPPOX, SOCK_DGRAM, PX_PROTO_OL2TP);\n\tif (sock < 0) {\n\t\tperror(\"socket\");\n\t\treturn 1;\n\t}\n\n\taddr.sa_family = AF_PPPOX;\n\taddr.sa_protocol = PX_PROTO_OL2TP;\n\taddr.pppol2tp.pid = 0;\n\taddr.pppol2tp.fd = sock;\n\taddr.pppol2tp.addr.sin_family = PF_INET;\n\taddr.pppol2tp.addr.sin_port = htons(0);\n\taddr.pppol2tp.addr.sin_addr.s_addr = inet_addr(\"192.168.0.1\");\n\taddr.pppol2tp.s_tunnel = 1;\n\taddr.pppol2tp.s_session = 0;\n\taddr.pppol2tp.d_tunnel = 0;\n\taddr.pppol2tp.d_session = 0;\n\n\tif (connect(sock, (const struct sockaddr *)&addr, sizeof(addr)) < 0) {\n\t\tperror(\"connect\");\n\t\treturn 1;\n\t}\n\n\treturn 0;\n}\n\nThis program causes the following lockdep warning:\n\n ============================================\n WARNING: possible recursive locking detected\n 6.2.0-rc5-00205-gc96618275234 #56 Not tainted\n --------------------------------------------\n repro/8607 is trying to acquire lock:\n ffff8880213c8130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: l2tp_tunnel_register+0x2b7/0x11c0\n\n but task is already holding lock:\n ffff8880213c8130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: pppol2tp_connect+0xa82/0x1a30\n\n other info that might help us debug this:\n Possible unsafe locking scenario:\n\n CPU0\n ----\n lock(sk_lock-AF_PPPOX);\n lock(sk_lock-AF_PPPOX);\n\n *** DEADLOCK ***\n\n May be due to missing lock nesting notation\n\n 1 lock held by repro/8607:\n #0: ffff8880213c8130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: pppol2tp_connect+0xa82/0x1a30\n\n stack backtrace:\n CPU: 0 PID: 8607 Comm: repro Not tainted 6.2.0-rc5-00205-gc96618275234 #56\n Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014\n Call Trace:\n \n dump_stack_lvl+0x100/0x178\n __lock_acquire.cold+0x119/0x3b9\n ? lockdep_hardirqs_on_prepare+0x410/0x410\n lock_acquire+0x1e0/0x610\n ? l2tp_tunnel_register+0x2b7/0x11c0\n ? lock_downgrade+0x710/0x710\n ? __fget_files+0x283/0x3e0\n lock_sock_nested+0x3a/0xf0\n ? l2tp_tunnel_register+0x2b7/0x11c0\n l2tp_tunnel_register+0x2b7/0x11c0\n ? sprintf+0xc4/0x100\n ? l2tp_tunnel_del_work+0x6b0/0x6b0\n ? debug_object_deactivate+0x320/0x320\n ? lockdep_init_map_type+0x16d/0x7a0\n ? lockdep_init_map_type+0x16d/0x7a0\n ? l2tp_tunnel_create+0x2bf/0x4b0\n ? l2tp_tunnel_create+0x3c6/0x4b0\n pppol2tp_connect+0x14e1/0x1a30\n ? pppol2tp_put_sk+0xd0/0xd0\n ? aa_sk_perm+0x2b7/0xa80\n ? aa_af_perm+0x260/0x260\n ? bpf_lsm_socket_connect+0x9/0x10\n ? pppol2tp_put_sk+0xd0/0xd0\n __sys_connect_file+0x14f/0x190\n __sys_connect+0x133/0x160\n ? __sys_connect_file+0x190/0x190\n ? lockdep_hardirqs_on+0x7d/0x100\n ? ktime_get_coarse_real_ts64+0x1b7/0x200\n ? ktime_get_coarse_real_ts64+0x147/0x200\n ? __audit_syscall_entry+0x396/0x500\n __x64_sys_connect+0x72/0xb0\n do_syscall_64+0x38/0xb0\n entry_SYSCALL_64_after_hwframe+0x63/0xcd\n\nThis patch fixes the issue by getting/creating the tunnel before\nlocking the pppol2tp socket.", "affected": [ { "vendor": "Linux", "product": "Linux", "defaultStatus": "unaffected", "versions": [ { "version": "2d77e5c0ad79004b5ef901895437e9cce6dfcc7e", "status": "affected", "versionType": "git", "lessThan": "4a413d360959962995e16a899cf2b9ef53e9fcb9" }, { "version": "77e8ed776cdb1a24b2aab8fe7c6f1f154235e1ce", "status": "affected", "versionType": "git", "lessThan": "f6df58aa15f7d469f69b1dd21b001ff483255244" }, { "version": "cef0845b6dcfa2f6c2c832e7f9622551456c741d", "status": "affected", "versionType": "git", "lessThan": "4bb736b40475528ac1aa8c98b368563618488a70" }, { "version": "0b2c59720e65885a394a017d0cf9cab118914682", "status": "affected", "versionType": "git", "lessThan": "5370647dd745bb3d8f37057006be207ddd8e9314" }, { "version": "0b2c59720e65885a394a017d0cf9cab118914682", "status": "affected", "versionType": "git", "lessThan": "9ca5e7ecab064f1f47da07f7c1ddf40e4bc0e5ac" }, { "version": "5.10.166", "status": "affected", "versionType": "semver", "lessThan": "5.10.173" }, { "version": "5.15.91", "status": "affected", "versionType": "semver", "lessThan": "5.15.99" }, { "version": "6.1.9", "status": "affected", "versionType": "semver", "lessThan": "6.1.16" } ] }, { "vendor": "Linux", "product": "Linux", "defaultStatus": "affected", "versions": [ { "version": "6.2", "status": "affected" }, { "version": "0", "status": "unaffected", "versionType": "semver", "lessThan": "6.2" }, { "version": "5.10.173", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.10.*" }, { "version": "5.15.99", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.15.*" }, { "version": "6.1.16", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.1.*" }, { "version": "6.2.3", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.2.*" }, { "version": "6.3", "status": "unaffected", "versionType": "original_commit_for_fix", "lessThanOrEqual": "*" } ] } ] } } }