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CVE-2026-63803 (GCVE-0-2026-63803)

Vulnerability from cvelistv5 – Published: 2026-07-19 12:02 – Updated: 2026-08-17 04:51
VLAI
Title
hdlc_ppp: sync per-proto timers before freeing hdlc state
Summary
In the Linux kernel, the following vulnerability has been resolved: hdlc_ppp: sync per-proto timers before freeing hdlc state Each PPP control protocol (LCP/IPCP/IPV6CP) embedded in struct ppp registers a timer via timer_setup(). That struct ppp is the hdlc->state allocation, which detach_hdlc_protocol() frees with kfree() in both teardown paths: unregister_hdlc_device() and the re-attach inside attach_hdlc_protocol(). The ppp proto never registered a .detach callback, so detach_hdlc_protocol() performs no timer synchronization before the kfree(). The only cancel, timer_delete(&proto->timer) in ppp_cp_event(), is partial (it does not wait for a running callback) and only runs on the ->CLOSED transition; ppp_stop()/ppp_close() do not sync either. A ppp_timer callback already executing (blocked on ppp->lock) survives the kfree and then dereferences proto->state / ppp->lock in freed memory, leading to a use-after-free. Fix this by adding a .detach helper that calls timer_shutdown_sync() on every per-proto timer. detach_hdlc_protocol() invokes proto->detach(dev) before kfree(hdlc->state), so timer_shutdown_sync() now runs on both free paths. timer_shutdown_sync() is used instead of timer_delete_sync() because the keepalive path re-arms the timer through add_timer()/mod_timer() and shutdown blocks any re-activation during teardown. Initialize the per-protocol timers in ppp_ioctl() when the protocol is attached, and remove the now-redundant timer_setup() from ppp_start(), so that the timers are initialized exactly once at attach time and ppp_timer_release() never operates on uninitialized timer_list structures. attach_hdlc_protocol() uses kmalloc() (not kzalloc), so struct ppp's protos[i].timer is uninitialized garbage until the first timer_setup(); without this init-at-attach, attaching the PPP protocol without ever bringing the device up would leave timer_shutdown_sync() operating on uninitialized memory in .detach. Moving the init out of ppp_start() (which only runs on NETDEV_UP) into the attach path makes the initialization unconditional and avoids initializing the same timer_list twice. This bug was found by static analysis.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 86d80a231bde4cfb64bfbfbfffd83056fc93628f (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 8308122bc9c065b1f376e081ed300129a2ac9545 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < ce8f9ddca0c9f217342a8b49efd309aa35b81a36 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 508a0139d3bf60f6a03d2fbfb63a89a9463d983a (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < c64dbef1c0fbd36f9530aa75112acdf6a6d3cfd8 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 5a84398101bf9f11e84b176343e4e3ba83e668c0 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < a594debfd4e7ec39413647458907f689ef57fd2f (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < c78a4e41ab5ead6193ad8a2dd92e8906bae659fa (git)
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Linux Linux Affected: 2.6.12
Unaffected: 0 , < 2.6.12 (semver)
Unaffected: 5.10.261 , ≤ 5.10.* (semver)
Unaffected: 5.15.211 , ≤ 5.15.* (semver)
Unaffected: 6.1.177 , ≤ 6.1.* (semver)
Unaffected: 6.6.144 , ≤ 6.6.* (semver)
Unaffected: 6.12.95 , ≤ 6.12.* (semver)
Unaffected: 6.18.38 , ≤ 6.18.* (semver)
Unaffected: 7.1.3 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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          "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-\u003estate 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(\u0026proto-\u003etimer) in ppp_cp_event(),\nis partial (it does not wait for a running callback) and only runs on the\n-\u003eCLOSED transition; ppp_stop()/ppp_close() do not sync either. A\nppp_timer callback already executing (blocked on ppp-\u003elock) survives the\nkfree and then dereferences proto-\u003estate / ppp-\u003elock 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-\u003edetach(dev)\nbefore kfree(hdlc-\u003estate), 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\u0027s 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."
        }
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              "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-\u003elock, 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-\u003elock 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."
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        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/86d80a231bde4cfb64bfbfbfffd83056fc93628f"
        },
        {
          "url": "https://git.kernel.org/stable/c/8308122bc9c065b1f376e081ed300129a2ac9545"
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      "title": "hdlc_ppp: sync per-proto timers before freeing hdlc state",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63803",
    "datePublished": "2026-07-19T12:02:08.574Z",
    "dateReserved": "2026-07-19T07:54:57.013Z",
    "dateUpdated": "2026-08-17T04:51:08.890Z",
    "state": "PUBLISHED"
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    "epss": {
      "cve": "CVE-2026-63803",
      "date": "2026-09-16",
      "epss": "0.00133",
      "percentile": "0.0318"
    },
    "microsoft_vex": {
      "current_release_date": "2026-08-14T18:26:51.000Z",
      "cve": "CVE-2026-63803",
      "id": "msrc_CVE-2026-63803",
      "initial_release_date": "2026-07-20T01:05:02.000Z",
      "product_status:fixed": "1",
      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "hdlc_ppp: sync per-proto timers before freeing hdlc state",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-63803.json",
      "version": "8"
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    "nvd": "{\"cve\":{\"id\":\"CVE-2026-63803\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-07-19T12:16:52.980\",\"lastModified\":\"2026-08-17T05:17:16.867\",\"vulnStatus\":\"Analyzed\",\"cveTags\":[],\"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-\u003estate 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(\u0026proto-\u003etimer) in ppp_cp_event(),\\nis partial (it does not wait for a running callback) and only runs on the\\n-\u003eCLOSED transition; ppp_stop()/ppp_close() do not sync either. A\\nppp_timer callback already executing (blocked on ppp-\u003elock) survives the\\nkfree and then dereferences proto-\u003estate / ppp-\u003elock 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-\u003edetach(dev)\\nbefore kfree(hdlc-\u003estate), 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\u0027s 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.\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"drivers/net/wan/hdlc_ppp.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"86d80a231bde4cfb64bfbfbfffd83056fc93628f\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"8308122bc9c065b1f376e081ed300129a2ac9545\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"ce8f9ddca0c9f217342a8b49efd309aa35b81a36\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"508a0139d3bf60f6a03d2fbfb63a89a9463d983a\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"c64dbef1c0fbd36f9530aa75112acdf6a6d3cfd8\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"5a84398101bf9f11e84b176343e4e3ba83e668c0\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"a594debfd4e7ec39413647458907f689ef57fd2f\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"c78a4e41ab5ead6193ad8a2dd92e8906bae659fa\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"drivers/net/wan/hdlc_ppp.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"2.6.12\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"2.6.12\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.10.261\",\"lessThanOrEqual\":\"5.10.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.15.211\",\"lessThanOrEqual\":\"5.15.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.1.177\",\"lessThanOrEqual\":\"6.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.6.144\",\"lessThanOrEqual\":\"6.6.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.12.95\",\"lessThanOrEqual\":\"6.12.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.18.38\",\"lessThanOrEqual\":\"6.18.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.1.3\",\"lessThanOrEqual\":\"7.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.2\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"type\":\"Secondary\",\"cvssData\":{\"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\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":1.8,\"impactScore\":5.9}]},\"weaknesses\":[{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-416\"}]}],\"configurations\":[{\"nodes\":[{\"operator\":\"OR\",\"negate\":false,\"cpeMatch\":[{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"2.6.12.1\",\"versionEndExcluding\":\"5.10.261\",\"matchCriteriaId\":\"957C42C7-357C-4EAA-BCE7-2A8821A5B248\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"5.11\",\"versionEndExcluding\":\"5.15.211\",\"matchCriteriaId\":\"D71C101E-388C-4A46-BD99-49049F7C5CFF\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"5.16\",\"versionEndExcluding\":\"6.1.177\",\"matchCriteriaId\":\"333C9E30-7FD4-46A2-94EF-C1AA1F3EE28B\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"6.2\",\"versionEndExcluding\":\"6.6.144\",\"matchCriteriaId\":\"C8AD3BC8-C843-423C-B9DB-CB52F67F578E\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"6.7\",\"versionEndExcluding\":\"6.12.95\",\"matchCriteriaId\":\"4E206B86-E0E3-4394-A93F-39F2D50A8AA8\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"6.13\",\"versionEndExcluding\":\"6.18.38\",\"matchCriteriaId\":\"FA591B28-5D62-449E-BDBE-3C9391BF070A\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-07-20T16:47:04+00:00",
      "cve": "CVE-2026-63803",
      "id": "CVE-2026-63803",
      "initial_release_date": "2026-07-19T00:00:00+00:00",
      "product_status:known_affected": "274",
      "product_status:known_not_affected": "1",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: hdlc_ppp: sync per-proto timers before freeing hdlc state",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63803.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-15T01:59:07Z",
      "cve": "CVE-2026-63803",
      "id": "CVE-2026-63803",
      "initial_release_date": "2026-07-19T17:35:02Z",
      "product_status:known_affected": "374",
      "product_status:recommended": "4",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-63803",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-63803.json",
      "version": "8"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.


Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.