CVE-2026-63981

{"id": "CVE-2026-63981", "cveTags": [], "metrics": {"cvssMetricV31": [{"type": "Primary", "source": "nvd@nist.gov", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 5.5, "attackVector": "LOCAL", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "integrityImpact": "NONE", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "HIGH", "privilegesRequired": "LOW", "confidentialityImpact": "NONE"}, "impactScore": 3.6, "exploitabilityScore": 1.8}]}, "affected": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "affectedData": [{"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "product": "Linux", "versions": [{"status": "affected", "version": "906736728cea480a85803c67fafb1b0e78491922", "lessThan": "25fc9352590f5ef21ebf290432bd768b336693bc", "versionType": "git"}, {"status": "affected", "version": "fe946a751d9b52b7c45ca34899723b314b79b249", "lessThan": "34457de389fb64a01fdcc71177dfebe65fd2d362", "versionType": "git"}, {"status": "affected", "version": "fe946a751d9b52b7c45ca34899723b314b79b249", "lessThan": "a005fa5d7502eefec7ee6e1c01adadc06de2f9ad", "versionType": "git"}], "programFiles": ["net/sched/act_mirred.c"], "defaultStatus": "unaffected"}, {"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "product": "Linux", "versions": [{"status": "affected", "version": "6.19"}, {"status": "unaffected", "version": "0", "lessThan": "6.19", "versionType": "semver"}, {"status": "unaffected", "version": "7.0.12", "versionType": "semver", "lessThanOrEqual": "7.0.*"}, {"status": "unaffected", "version": "7.1", "versionType": "original_commit_for_fix", "lessThanOrEqual": "*"}], "programFiles": ["net/sched/act_mirred.c"], "defaultStatus": "affected"}]}], "published": "2026-07-19T16:17:17.283", "references": [{"url": "https://git.kernel.org/stable/c/25fc9352590f5ef21ebf290432bd768b336693bc", "tags": ["Patch"], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/34457de389fb64a01fdcc71177dfebe65fd2d362", "tags": ["Patch"], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/a005fa5d7502eefec7ee6e1c01adadc06de2f9ad", "tags": ["Patch"], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}], "vulnStatus": "Analyzed", "weaknesses": [{"type": "Primary", "source": "nvd@nist.gov", "description": [{"lang": "en", "value": "CWE-674"}]}], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: act_mirred: Fix blockcast recursion bypass leading to stack overflow\n\ntcf_mirred_act() checks sched_mirred_nest against MIRRED_NEST_LIMIT (4)\nto prevent deep recursion. However, when the action uses blockcast\n(tcfm_blockid != 0), the function returns at the tcf_blockcast() call\nBEFORE reaching the counter increment. As a result, the recursion\ncounter never advances and the limit check is entirely bypassed.\n\nWhen two devices share a TC egress block with a mirred blockcast rule,\na packet egressing on device A is mirrored to device B via blockcast;\ndevice B's egress TC re-enters tcf_mirred_act() via blockcast and\nmirrors back to A, creating an unbounded recursion loop:\n\n tcf_mirred_act -> tcf_blockcast -> tcf_mirred_to_dev -> dev_queue_xmit\n -> sch_handle_egress -> tcf_classify -> tcf_mirred_act -> (repeat)\n\nThis recursion continues until the kernel stack overflows.\n\nThe bug is reachable from an unprivileged user via\nunshare(CLONE_NEWUSER | CLONE_NEWNET): user namespaces grant\nCAP_NET_ADMIN in the new network namespace, which is sufficient to\ncreate dummy devices, attach clsact qdiscs with shared blocks, and\ninstall mirred blockcast filters.\n\n BUG: TASK stack guard page was hit at ffffc90000b7fff8\n Oops: stack guard page: 0000 [#1] SMP KASAN NOPTI\n CPU: 2 UID: 1000 PID: 169 Comm: poc Not tainted 7.0.0-rc7-next-20260410\n RIP: 0010:xas_find+0x17/0x480\n Call Trace:\n xa_find+0x17b/0x1d0\n tcf_mirred_act+0x640/0x1060\n tcf_action_exec+0x400/0x530\n basic_classify+0x128/0x1d0\n tcf_classify+0xd83/0x1150\n tc_run+0x328/0x620\n __dev_queue_xmit+0x797/0x3100\n tcf_mirred_to_dev+0x7b1/0xf70\n tcf_mirred_act+0x68a/0x1060\n [repeating ~30+ times until stack overflow]\n Kernel panic - not syncing: Fatal exception in interrupt\n\nFix this by incrementing sched_mirred_nest before calling\ntcf_blockcast() and decrementing it on return, mirroring the\nnon-blockcast path. This ensures subsequent recursive entries see the\nupdated counter and are correctly limited by MIRRED_NEST_LIMIT."}], "lastModified": "2026-11-12T17:34:44.060", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "9161A938-0FA8-44BC-95FE-C5A271601AB3", "versionEndExcluding": "7.0.12", "versionStartIncluding": "6.19"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc1:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "B1EF7059-E670-45F4-B422-54C40FA86390"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc2:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "0D38F0BF-A728-4133-A358-D44A2F7EE6D6"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc3:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "EC732D08-5F7B-46D9-B154-E60C7F4F0A97"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc4:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "E5910A9D-F60A-409A-B486-FE66BFEBA9B9"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc5:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "81DFF19E-9CF8-49C6-8C36-1E4038622933"}], "operator": "OR"}]}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}