{"id":"CVE-2021-4454","title":"In the Linux kernel, the following vulnerability has been resolved:\n\ncan: j1939: fix errant WARN_ON_ONCE in j1939_session_deactivate\n\nThe conclusion \"j1939_session_deactivate() should be called with a\nsession ref-count of at least 2\" is …","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\ncan: j1939: fix errant WARN_ON_ONCE in j1939_session_deactivate\n\nThe conclusion \"j1939_session_deactivate() should be called with a\nsession ref-count of at least 2\" is …","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","cwe":["CWE-20"],"vendor":"linux","product":"linux_kernel","affected":["linux_kernel >= 5.4.138, < 5.4.232","linux_kernel >= 5.10.56, < 5.10.168","linux_kernel >= 5.13.8, < 5.14","linux_kernel >= 5.14.1, < 5.15.93","linux_kernel >= 5.16, < 6.1.11","linux_kernel = 5.14","linux_kernel = 6.2"],"patched":["linux_kernel 6.1.11"],"published":"2025-03-27","updated":"2026-10-15","sourceUpdated":"2026-10-15T22:17:22.303","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2021-4454","references":[{"url":"https://git.kernel.org/stable/c/1740a1e45eee65099a92fb502e1e67e63aad277d","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/6950df42a03c9ac9290503ced3f371199cb68fa9","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/9ab896775f98ff54b68512f345eed178bf961084","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/b6d44072117bba057d50f7a2f96e5d070c65926d","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/d0553680f94c49bbe0e39eb50d033ba563b4212d","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2021/cve-2021-4454.json"},{"url":"https://access.redhat.com/security/cve/CVE-2021-4454"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2355529"},{"url":"https://www.cve.org/CVERecord?id=CVE-2021-4454"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-4454"},{"url":"https://lore.kernel.org/linux-cve-announce/2025032716-CVE-2021-4454-f4a4@gregkh/T"}],"tags":["nvd","csaf","vex","red-hat","cve.org","score-dispute"],"epss":0.00591,"epssPercentile":0.48037,"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"partial","timestamp":"2026-10-15T21:02:43.206452Z"},"scores":{"nvd":7.5,"vendor":3.3,"cna":7.5},"ingestedAt":"2026-10-15T21:45:11.292Z","slug":"CVE-2021-4454","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\ncan: j1939: fix errant WARN_ON_ONCE in j1939_session_deactivate\n\nThe conclusion \"j1939_session_deactivate() should be called with a\nsession ref-count of at least 2\" is incorrect. In some concurrent\nscenarios, j1939_session_deactivate can be called with the session\nref-count less than 2. But there is not any problem because it\nwill check the session active state before session putting in\nj1939_session_deactivate_locked().\n\nHere is the concurrent scenario of the problem reported by syzbot\nand my reproduction log.\n\n        cpu0                            cpu1\n                                j1939_xtp_rx_eoma\nj1939_xtp_rx_abort_one\n                                j1939_session_get_by_addr [kref == 2]\nj1939_session_get_by_addr [kref == 3]\nj1939_session_deactivate [kref == 2]\nj1939_session_put [kref == 1]\n\t\t\t\tj1939_session_completed\n\t\t\t\tj1939_session_deactivate\n\t\t\t\tWARN_ON_ONCE(kref < 2)\n\n=====================================================\nWARNING: CPU: 1 PID: 21 at net/can/j1939/transport.c:1088 j1939_session_deactivate+0x5f/0x70\nCPU: 1 PID: 21 Comm: ksoftirqd/1 Not tainted 5.14.0-rc7+ #32\nHardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1 04/01/2014\nRIP: 0010:j1939_session_deactivate+0x5f/0x70\nCall Trace:\n j1939_session_deactivate_activate_next+0x11/0x28\n j1939_xtp_rx_eoma+0x12a/0x180\n j1939_tp_recv+0x4a2/0x510\n j1939_can_recv+0x226/0x380\n can_rcv_filter+0xf8/0x220\n can_receive+0x102/0x220\n ? process_backlog+0xf0/0x2c0\n can_rcv+0x53/0xf0\n __netif_receive_skb_one_core+0x67/0x90\n ? process_backlog+0x97/0x2c0\n __netif_receive_skb+0x22/0x80\n\n## Affected\n\n- `linux_kernel >= 5.4.138, < 5.4.232`\n- `linux_kernel >= 5.10.56, < 5.10.168`\n- `linux_kernel >= 5.13.8, < 5.14`\n- `linux_kernel >= 5.14.1, < 5.15.93`\n- `linux_kernel >= 5.16, < 6.1.11`\n- `linux_kernel = 5.14`\n- `linux_kernel = 6.2`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `linux_kernel 6.1.11`\n\n## Vendor advisories\n\n- **Red Hat VEX** · Low · affected: Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 9 · updated 2026-10-16 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2021/cve-2021-4454.json)","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[{"seq":230003,"id":"CVE-2021-4454","ts":1793124768327,"field":"cvss","old":"3.3","new":"7.5"},{"seq":230002,"id":"CVE-2021-4454","ts":1793124768327,"field":"severity","old":"low","new":"high"},{"seq":223801,"id":"CVE-2021-4454","ts":1792238433342,"field":"cvss","old":"7.5","new":"3.3"},{"seq":223800,"id":"CVE-2021-4454","ts":1792238433342,"field":"severity","old":"high","new":"low"}]}