CVE-2026-63918

{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-63918", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-07-19T07:54:57.020Z", "datePublished": "2026-07-19T14:55:21.414Z", "dateUpdated": "2026-08-05T12:37:12.656Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:37:12.656Z"}, "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nl2tp: use refcount_inc_not_zero in l2tp_session_get_by_ifname\n\nA reader in l2tp_session_get_by_ifname() can return a pointer to a\nsession whose refcount has reached zero. The getter takes its\nreference with plain refcount_inc(), but every other session getter\nin the same file (l2tp_v2_session_get, l2tp_v3_session_get, and the\ncorresponding _get_next variants) uses refcount_inc_not_zero()\nbecause the IDR/RCU lookup can race with refcount_dec_and_test() ->\nl2tp_session_free() -> kfree_rcu(). The ifname getter is the only\noutlier; the inconsistency was raised on-list after 979c017803c4\n(\"l2tp: use list_del_rcu in l2tp_session_unhash\").\n\nA reader inside rcu_read_lock_bh() that matches session->ifname can\nbe preempted between the strcmp() and the refcount_inc(). If the\nlast reference drops on another CPU in that window, the reader's\nrefcount_inc() runs on a counter that has reached zero. refcount_t\ncatches the addition-on-zero, prints \"refcount_t: addition on 0;\nuse-after-free\", saturates the counter, and returns the saturated\npointer to the caller. Session memory is held live by the in-flight\nRCU read section, but the kfree_rcu() callback queued from\nl2tp_session_free() will free it once the grace period closes; a\ncaller that dereferences the returned session past that point hits\na slab-use-after-free. On PREEMPT_RT local_bh_disable() is a per-CPU\nsleeping lock and the preemption window is real; on stock PREEMPT\nkernels local_bh_disable() is a preempt_count increment that closes\nthe cross-CPU race in practice (see below).\n\nUse refcount_inc_not_zero() and continue the list walk on failure,\nmatching the other session getters in the file. The ifname getter\nis the only session getter in net/l2tp/ that still uses the bare\nrefcount_inc() pattern; this change restores file-internal\nconsistency. The success path is unchanged."}], "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 vulnerable code is only reached via the L2TP genetlink management API (netlink syscall), not from the L2TP data-plane packet receive path. Attackers must issue local netlink commands such as SESSION_GET, SESSION_DELETE, or SESSION_MODIFY with L2TP_ATTR_IFNAME.\nAC:L - Exploitation requires racing session lookup-by-ifname against concurrent session deletion, and an attacker with CAP_NET_ADMIN can control both sides by issuing parallel netlink operations. On PREEMPT_RT kernels the preemption window between strcmp() and refcount_inc() is real and reliably winnable.\nPR:L - All affected genetlink commands are gated by GENL_UNS_ADMIN_PERM, requiring CAP_NET_ADMIN in the network namespace. That capability is obtainable by unprivileged users via user/network namespaces (unshare -Urn), not only by init-namespace root.\nUI:N - No victim interaction is required; the attacker triggers the race directly through netlink management commands without needing another user to mount, open, or configure anything.\nS:U - Impact is confined to kernel memory corruption and privilege escalation within the same kernel security domain. This is not a VM escape, sandbox boundary cross, or IOMMU bypass.\nC:H - The bug is a slab use-after-free on struct l2tp_session; returning and later dereferencing a session whose refcount reached zero enables reading freed kernel heap memory and leaking kernel pointers or other sensitive data.\nI:H - UAF on struct l2tp_session corrupts a heap object that contains function pointers (recv_skb, session_close) and is subsequently used by session_delete/modify/notify handlers, enabling arbitrary kernel write or code execution via heap grooming.\nA:H - Dereferencing the freed l2tp_session after the RCU grace period causes kernel oops or panic. Even failed exploitation attempts trigger refcount_t \"addition on 0; use-after-free\" warnings and can crash the system under load."}]}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["net/l2tp/l2tp_core.c"], "versions": [{"version": "abe7a1a7d0b69e63b1bca5f9531023a52336784f", "lessThan": "ee80455feffb9cb62b5b58715cabeff495e666b2", "status": "affected", "versionType": "git"}, {"version": "abe7a1a7d0b69e63b1bca5f9531023a52336784f", "lessThan": "947013fd7c8c35dd5856557b215840098a3f67f8", "status": "affected", "versionType": "git"}, {"version": "abe7a1a7d0b69e63b1bca5f9531023a52336784f", "lessThan": "782d60a6596aee9b29c2eecfa70033899278bf65", "status": "affected", "versionType": "git"}, {"version": "abe7a1a7d0b69e63b1bca5f9531023a52336784f", "lessThan": "05f95729ca844704d15e49ce14868af4b403b32b", "status": "affected", "versionType": "git"}]}, {"product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["net/l2tp/l2tp_core.c"], "versions": [{"version": "6.12", "status": "affected"}, {"version": "0", "lessThan": "6.12", "status": "unaffected", "versionType": "semver"}, {"version": "6.12.93", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.18.35", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.0.12", "lessThanOrEqual": "7.0.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.1", "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": "6.12", "versionEndExcluding": "6.12.93"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.12", "versionEndExcluding": "6.18.35"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.12", "versionEndExcluding": "7.0.12"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.12", "versionEndExcluding": "7.1"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/ee80455feffb9cb62b5b58715cabeff495e666b2"}, {"url": "https://git.kernel.org/stable/c/947013fd7c8c35dd5856557b215840098a3f67f8"}, {"url": "https://git.kernel.org/stable/c/782d60a6596aee9b29c2eecfa70033899278bf65"}, {"url": "https://git.kernel.org/stable/c/05f95729ca844704d15e49ce14868af4b403b32b"}], "title": "l2tp: use refcount_inc_not_zero in l2tp_session_get_by_ifname", "x_generator": {"engine": "bippy-1.2.0"}}}}

{}

{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "product": "Linux", "programFiles": ["net/l2tp/l2tp_core.c"], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "versions": [{"lessThan": "ee80455feffb9cb62b5b58715cabeff495e666b2", "status": "affected", "version": "abe7a1a7d0b69e63b1bca5f9531023a52336784f", "versionType": "git"}, {"lessThan": "947013fd7c8c35dd5856557b215840098a3f67f8", "status": "affected", "version": "abe7a1a7d0b69e63b1bca5f9531023a52336784f", "versionType": "git"}, {"lessThan": "782d60a6596aee9b29c2eecfa70033899278bf65", "status": "affected", "version": "abe7a1a7d0b69e63b1bca5f9531023a52336784f", "versionType": "git"}, {"lessThan": "05f95729ca844704d15e49ce14868af4b403b32b", "status": "affected", "version": "abe7a1a7d0b69e63b1bca5f9531023a52336784f", "versionType": "git"}]}, {"defaultStatus": "affected", "product": "Linux", "programFiles": ["net/l2tp/l2tp_core.c"], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "versions": [{"status": "affected", "version": "6.12"}, {"lessThan": "6.12", "status": "unaffected", "version": "0", "versionType": "semver"}, {"lessThanOrEqual": "6.12.*", "status": "unaffected", "version": "6.12.93", "versionType": "semver"}, {"lessThanOrEqual": "6.18.*", "status": "unaffected", "version": "6.18.35", "versionType": "semver"}, {"lessThanOrEqual": "7.0.*", "status": "unaffected", "version": "7.0.12", "versionType": "semver"}, {"lessThanOrEqual": "*", "status": "unaffected", "version": "7.1", "versionType": "original_commit_for_fix"}]}], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}], "configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "2FBF8AA6-5161-4A17-A648-F77C9EB340CA", "versionEndExcluding": "6.12.93", "versionStartIncluding": "6.12", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "0FCCB23A-7629-4386-93B6-B119237C4382", "versionEndExcluding": "6.18.35", "versionStartIncluding": "6.13", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "9161A938-0FA8-44BC-95FE-C5A271601AB3", "versionEndExcluding": "7.0.12", "versionStartIncluding": "6.19", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc1:*:*:*:*:*:*", "matchCriteriaId": "B1EF7059-E670-45F4-B422-54C40FA86390", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc2:*:*:*:*:*:*", "matchCriteriaId": "0D38F0BF-A728-4133-A358-D44A2F7EE6D6", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc3:*:*:*:*:*:*", "matchCriteriaId": "EC732D08-5F7B-46D9-B154-E60C7F4F0A97", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc4:*:*:*:*:*:*", "matchCriteriaId": "E5910A9D-F60A-409A-B486-FE66BFEBA9B9", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc5:*:*:*:*:*:*", "matchCriteriaId": "81DFF19E-9CF8-49C6-8C36-1E4038622933", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nl2tp: use refcount_inc_not_zero in l2tp_session_get_by_ifname\n\nA reader in l2tp_session_get_by_ifname() can return a pointer to a\nsession whose refcount has reached zero. The getter takes its\nreference with plain refcount_inc(), but every other session getter\nin the same file (l2tp_v2_session_get, l2tp_v3_session_get, and the\ncorresponding _get_next variants) uses refcount_inc_not_zero()\nbecause the IDR/RCU lookup can race with refcount_dec_and_test() ->\nl2tp_session_free() -> kfree_rcu(). The ifname getter is the only\noutlier; the inconsistency was raised on-list after 979c017803c4\n(\"l2tp: use list_del_rcu in l2tp_session_unhash\").\n\nA reader inside rcu_read_lock_bh() that matches session->ifname can\nbe preempted between the strcmp() and the refcount_inc(). If the\nlast reference drops on another CPU in that window, the reader's\nrefcount_inc() runs on a counter that has reached zero. refcount_t\ncatches the addition-on-zero, prints \"refcount_t: addition on 0;\nuse-after-free\", saturates the counter, and returns the saturated\npointer to the caller. Session memory is held live by the in-flight\nRCU read section, but the kfree_rcu() callback queued from\nl2tp_session_free() will free it once the grace period closes; a\ncaller that dereferences the returned session past that point hits\na slab-use-after-free. On PREEMPT_RT local_bh_disable() is a per-CPU\nsleeping lock and the preemption window is real; on stock PREEMPT\nkernels local_bh_disable() is a preempt_count increment that closes\nthe cross-CPU race in practice (see below).\n\nUse refcount_inc_not_zero() and continue the list walk on failure,\nmatching the other session getters in the file. The ifname getter\nis the only session getter in net/l2tp/ that still uses the bare\nrefcount_inc() pattern; this change restores file-internal\nconsistency. The success path is unchanged."}], "id": "CVE-2026-63918", "lastModified": "2026-10-30T14:29:17.460", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "LOCAL", "availabilityImpact": "HIGH", "baseScore": 7.8, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "version": "3.1"}, "exploitabilityScore": 1.8, "impactScore": 5.9, "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary"}]}, "published": "2026-07-19T16:17:09.917", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/05f95729ca844704d15e49ce14868af4b403b32b"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/782d60a6596aee9b29c2eecfa70033899278bf65"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/947013fd7c8c35dd5856557b215840098a3f67f8"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/ee80455feffb9cb62b5b58715cabeff495e666b2"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-416"}], "source": "nvd@nist.gov", "type": "Primary"}]}

{"bugzilla": {"description": "kernel: l2tp: use refcount_inc_not_zero in l2tp_session_get_by_ifname", "id": "2502384", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2502384"}, "csaw": false, "cvss3": {"cvss3_base_score": "7.0", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H", "status": "draft"}, "cwe": "CWE-911", "details": ["A flaw was found in the Linux kernel's Layer 2 Tunneling Protocol (l2tp) module. A race condition exists where a network session's memory could be prematurely released while still in use. This vulnerability, caused by incorrect reference counting, may allow a local attacker to trigger a system crash (denial of service) or potentially execute unauthorized code."], "name": "CVE-2026-63918", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 10"}, {"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 9"}], "public_date": "2026-07-19T00:00:00Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-63918\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-63918\nhttps://lore.kernel.org/linux-cve-announce/2026071947-CVE-2026-63918-2288@gregkh/T"], "threat_severity": "Moderate"}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[abe7a1a7d0b69e63b1bca5f9531023a52336784f,ee80455feffb9cb62b5b58715cabeff495e666b2)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[abe7a1a7d0b69e63b1bca5f9531023a52336784f,947013fd7c8c35dd5856557b215840098a3f67f8)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[abe7a1a7d0b69e63b1bca5f9531023a52336784f,782d60a6596aee9b29c2eecfa70033899278bf65)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[abe7a1a7d0b69e63b1bca5f9531023a52336784f,05f95729ca844704d15e49ce14868af4b403b32b)"}}], "enrichment": {"confidence": 99.0, "confidence_source": "inferred", "scores": [{"score": 99.0, "source": "inferred"}, {"score": 100.0, "source": "matching"}]}, "original": {"product": "Linux", "source": "cna", "vendor": "Linux"}, "product": "linux_kernel", "vendor": "linux"}, {"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "6.12"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "[0,6.12)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "[6.12.93,6.13.0)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "[6.18.35,6.19.0)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "[7.0.12,7.1.0)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "[7.1,*]"}}], "enrichment": {"confidence": 99.0, "confidence_source": "inferred", "scores": [{"score": 99.0, "source": "inferred"}, {"score": 100.0, "source": "matching"}]}, "original": {"product": "Linux", "source": "cna", "vendor": "Linux"}, "product": "linux_kernel", "vendor": "linux"}], "created": "2026-07-21T04:45:02.591017+00:00", "updated": "2026-10-30T16:15:14.985609+00:00", "vendors": ["linux", "linux$PRODUCT$linux_kernel"]}