{"id":"CVE-2026-23319","title":"bpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim\n\nThe root cause of this bug is that when 'bpf_link_put' reduces the\nrefcount of 'shim_link->link.link' to zero, …","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e < 529e685e522b9d7fb379dbe6929dcdf520e34c8c","Linux >= 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e < 9b02c5c4147f8af8ed783c8deb5df927a55c3951","Linux >= 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e < cfcfa0ca0212162aa472551266038e8fd6768cff","Linux >= 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e < 3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2","Linux >= 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e < 4e8a0005d633a4adc98e3b65d5080f93b90d356b","Linux >= 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e < 56145d237385ca0e7ca9ff7b226aaf2eb8ef368b","Linux 6.0"],"published":"2026-03-25","updated":"2026-09-08","sourceUpdated":"2026-09-08T08:45:34.382Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-23319","references":[{"url":"https://git.kernel.org/stable/c/529e685e522b9d7fb379dbe6929dcdf520e34c8c"},{"url":"https://git.kernel.org/stable/c/9b02c5c4147f8af8ed783c8deb5df927a55c3951"},{"url":"https://git.kernel.org/stable/c/cfcfa0ca0212162aa472551266038e8fd6768cff"},{"url":"https://git.kernel.org/stable/c/3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2"},{"url":"https://git.kernel.org/stable/c/4e8a0005d633a4adc98e3b65d5080f93b90d356b"},{"url":"https://git.kernel.org/stable/c/56145d237385ca0e7ca9ff7b226aaf2eb8ef368b"}],"tags":["cve.org"],"epss":0.00126,"epssPercentile":0.02602,"ingestedAt":"2026-09-08T15:33:26.993Z","slug":"CVE-2026-23319","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim\n\nThe root cause of this bug is that when 'bpf_link_put' reduces the\nrefcount of 'shim_link->link.link' to zero, the resource is considered\nreleased but may still be referenced via 'tr->progs_hlist' in\n'cgroup_shim_find'. The actual cleanup of 'tr->progs_hlist' in\n'bpf_shim_tramp_link_release' is deferred. During this window, another\nprocess can cause a use-after-free via 'bpf_trampoline_link_cgroup_shim'.\n\nBased on Martin KaFai Lau's suggestions, I have created a simple patch.\n\nTo fix this:\n   Add an atomic non-zero check in 'bpf_trampoline_link_cgroup_shim'.\n   Only increment the refcount if it is not already zero.\n\nTesting:\n   I verified the fix by adding a delay in\n   'bpf_shim_tramp_link_release' to make the bug easier to trigger:\n\nstatic void bpf_shim_tramp_link_release(struct bpf_link *link)\n{\n\t/* ... */\n\tif (!shim_link->trampoline)\n\t\treturn;\n\n+\tmsleep(100);\n\tWARN_ON_ONCE(bpf_trampoline_unlink_prog(&shim_link->link,\n\t\tshim_link->trampoline, NULL));\n\tbpf_trampoline_put(shim_link->trampoline);\n}\n\nBefore the patch, running a PoC easily reproduced the crash(almost 100%)\nwith a call trace similar to KaiyanM's report.\nAfter the patch, the bug no longer occurs even after millions of\niterations.\n\n## Affected\n\n- `Linux >= 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e < 529e685e522b9d7fb379dbe6929dcdf520e34c8c`\n- `Linux >= 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e < 9b02c5c4147f8af8ed783c8deb5df927a55c3951`\n- `Linux >= 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e < cfcfa0ca0212162aa472551266038e8fd6768cff`\n- `Linux >= 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e < 3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2`\n- `Linux >= 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e < 4e8a0005d633a4adc98e3b65d5080f93b90d356b`\n- `Linux >= 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e < 56145d237385ca0e7ca9ff7b226aaf2eb8ef368b`\n- `Linux 6.0`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}