{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-63803","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2026-07-19T07:54:57.013Z","datePublished":"2026-07-19T12:02:08.574Z","dateUpdated":"2026-08-17T04:51:08.890Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-17T04:51:08.890Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nhdlc_ppp: sync per-proto timers before freeing hdlc state\n\nEach PPP control protocol (LCP/IPCP/IPV6CP) embedded in struct ppp\nregisters a timer via timer_setup(). That struct ppp is the\nhdlc->state allocation, which detach_hdlc_protocol() frees with kfree()\nin both teardown paths: unregister_hdlc_device() and the re-attach inside\nattach_hdlc_protocol().\n\nThe ppp proto never registered a .detach callback, so\ndetach_hdlc_protocol() performs no timer synchronization before the\nkfree(). The only cancel, timer_delete(&proto->timer) in ppp_cp_event(),\nis partial (it does not wait for a running callback) and only runs on the\n->CLOSED transition; ppp_stop()/ppp_close() do not sync either. A\nppp_timer callback already executing (blocked on ppp->lock) survives the\nkfree and then dereferences proto->state / ppp->lock in freed memory,\nleading to a use-after-free.\n\nFix this by adding a .detach helper that calls timer_shutdown_sync() on\nevery per-proto timer. detach_hdlc_protocol() invokes proto->detach(dev)\nbefore kfree(hdlc->state), so timer_shutdown_sync()\nnow runs on both free paths.\ntimer_shutdown_sync() is used instead of timer_delete_sync() because the\nkeepalive path re-arms the timer through add_timer()/mod_timer() and\nshutdown blocks any re-activation during teardown.\n\nInitialize the per-protocol timers in ppp_ioctl() when the protocol is\nattached, and remove the now-redundant timer_setup() from ppp_start(), so\nthat the timers are initialized exactly once at attach time and\nppp_timer_release() never operates on uninitialized timer_list\nstructures. attach_hdlc_protocol() uses kmalloc() (not kzalloc), so\nstruct ppp's protos[i].timer is uninitialized garbage until the first\ntimer_setup(); without this init-at-attach, attaching the PPP protocol\nwithout ever bringing the device up would leave timer_shutdown_sync()\noperating on uninitialized memory in .detach. Moving the init out of\nppp_start() (which only runs on NETDEV_UP) into the attach path makes the\ninitialization unconditional and avoids initializing the same timer_list\ntwice.\n\nThis bug was found by static analysis."}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The UAF occurs in detach_hdlc_protocol() during protocol teardown via SIOCWANDEV ioctl or driver unregister, not during packet receive. Remote PPP peers can influence timers but cannot reach the kfree() path without local CAP_NET_ADMIN configuration actions.\nAC:L - An attacker with CAP_NET_ADMIN can reliably trigger the bug by bringing a PPP HDLC interface up (arming timers via ppp_start/LCP), then tearing down or re-attaching the protocol while timers are pending or a ppp_timer callback is blocked on ppp->lock, controlling both sides of the race.\nPR:L - Exploitation requires CAP_NET_ADMIN to attach/detach the PPP protocol via SIOCWANDEV (ppp_ioctl checks capable(CAP_NET_ADMIN)), which is reachable by unprivileged users who create user namespaces with CAP_NET_ADMIN per kernel CVSS guidance.\nUI:N - No victim interaction is required once the attacker has network administration capability on a system with an HDLC WAN device; exploitation is fully attacker-driven through ioctl and interface up/down operations.\nS:U - The use-after-free corrupts kernel heap memory within the same kernel security boundary, enabling local privilege escalation rather than crossing a VM, container, or IOMMU security boundary.\nC:H - Use-after-free of struct ppp and its embedded spinlock_t allows dereferencing attacker-influenced freed heap memory, which can be leveraged for arbitrary kernel memory read via heap grooming and controlled reuse of the freed slab object.\nI:H - The UAF on struct ppp and ppp->lock provides a standard kernel heap corruption primitive that can be developed into arbitrary write and local privilege escalation through control of reallocated object contents and spinlock corruption.\nA:H - The freed-memory dereference in ppp_timer() causes kernel oops or panic during protocol teardown, and repeated triggering during interface reconfiguration can cause sustained denial of service on WAN router systems."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/wan/hdlc_ppp.c"],"versions":[{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","lessThan":"86d80a231bde4cfb64bfbfbfffd83056fc93628f","status":"affected","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","lessThan":"8308122bc9c065b1f376e081ed300129a2ac9545","status":"affected","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","lessThan":"ce8f9ddca0c9f217342a8b49efd309aa35b81a36","status":"affected","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","lessThan":"508a0139d3bf60f6a03d2fbfb63a89a9463d983a","status":"affected","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","lessThan":"c64dbef1c0fbd36f9530aa75112acdf6a6d3cfd8","status":"affected","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","lessThan":"5a84398101bf9f11e84b176343e4e3ba83e668c0","status":"affected","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","lessThan":"a594debfd4e7ec39413647458907f689ef57fd2f","status":"affected","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","lessThan":"c78a4e41ab5ead6193ad8a2dd92e8906bae659fa","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/wan/hdlc_ppp.c"],"versions":[{"version":"2.6.12","status":"affected"},{"version":"0","lessThan":"2.6.12","status":"unaffected","versionType":"semver"},{"version":"5.10.261","lessThanOrEqual":"5.10.*","status":"unaffected","versionType":"semver"},{"version":"5.15.211","lessThanOrEqual":"5.15.*","status":"unaffected","versionType":"semver"},{"version":"6.1.177","lessThanOrEqual":"6.1.*","status":"unaffected","versionType":"semver"},{"version":"6.6.144","lessThanOrEqual":"6.6.*","status":"unaffected","versionType":"semver"},{"version":"6.12.95","lessThanOrEqual":"6.12.*","status":"unaffected","versionType":"semver"},{"version":"6.18.38","lessThanOrEqual":"6.18.*","status":"unaffected","versionType":"semver"},{"version":"7.1.3","lessThanOrEqual":"7.1.*","status":"unaffected","versionType":"semver"},{"version":"7.2","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":"5.10.261"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.12","versionEndExcluding":"5.15.211"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.12","versionEndExcluding":"6.1.177"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.12","versionEndExcluding":"6.6.144"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.12","versionEndExcluding":"6.12.95"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.12","versionEndExcluding":"6.18.38"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.12","versionEndExcluding":"7.1.3"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.12","versionEndExcluding":"7.2"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/86d80a231bde4cfb64bfbfbfffd83056fc93628f"},{"url":"https://git.kernel.org/stable/c/8308122bc9c065b1f376e081ed300129a2ac9545"},{"url":"https://git.kernel.org/stable/c/ce8f9ddca0c9f217342a8b49efd309aa35b81a36"},{"url":"https://git.kernel.org/stable/c/508a0139d3bf60f6a03d2fbfb63a89a9463d983a"},{"url":"https://git.kernel.org/stable/c/c64dbef1c0fbd36f9530aa75112acdf6a6d3cfd8"},{"url":"https://git.kernel.org/stable/c/5a84398101bf9f11e84b176343e4e3ba83e668c0"},{"url":"https://git.kernel.org/stable/c/a594debfd4e7ec39413647458907f689ef57fd2f"},{"url":"https://git.kernel.org/stable/c/c78a4e41ab5ead6193ad8a2dd92e8906bae659fa"}],"title":"hdlc_ppp: sync per-proto timers before freeing hdlc state","x_generator":{"engine":"bippy-1.2.0"}}}}