FKIE_CVE-2026-23319

Vulnerability from fkie_nvd - Published: 2026-03-25 11:16 - Updated: 2026-04-23 21:05
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim The root cause of this bug is that when 'bpf_link_put' reduces the refcount of 'shim_link->link.link' to zero, the resource is considered released but may still be referenced via 'tr->progs_hlist' in 'cgroup_shim_find'. The actual cleanup of 'tr->progs_hlist' in 'bpf_shim_tramp_link_release' is deferred. During this window, another process can cause a use-after-free via 'bpf_trampoline_link_cgroup_shim'. Based on Martin KaFai Lau's suggestions, I have created a simple patch. To fix this: Add an atomic non-zero check in 'bpf_trampoline_link_cgroup_shim'. Only increment the refcount if it is not already zero. Testing: I verified the fix by adding a delay in 'bpf_shim_tramp_link_release' to make the bug easier to trigger: static void bpf_shim_tramp_link_release(struct bpf_link *link) { /* ... */ if (!shim_link->trampoline) return; + msleep(100); WARN_ON_ONCE(bpf_trampoline_unlink_prog(&shim_link->link, shim_link->trampoline, NULL)); bpf_trampoline_put(shim_link->trampoline); } Before the patch, running a PoC easily reproduced the crash(almost 100%) with a call trace similar to KaiyanM's report. After the patch, the bug no longer occurs even after millions of iterations.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/4e8a0005d633a4adc98e3b65d5080f93b90d356bPatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/529e685e522b9d7fb379dbe6929dcdf520e34c8cPatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/56145d237385ca0e7ca9ff7b226aaf2eb8ef368bPatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/9b02c5c4147f8af8ed783c8deb5df927a55c3951Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/cfcfa0ca0212162aa472551266038e8fd6768cffPatch
Impacted products
Vendor Product Version
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
linux linux_kernel 6.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
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      "lang": "en",
      "value": "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 \u0027bpf_link_put\u0027 reduces the\nrefcount of \u0027shim_link-\u003elink.link\u0027 to zero, the resource is considered\nreleased but may still be referenced via \u0027tr-\u003eprogs_hlist\u0027 in\n\u0027cgroup_shim_find\u0027. The actual cleanup of \u0027tr-\u003eprogs_hlist\u0027 in\n\u0027bpf_shim_tramp_link_release\u0027 is deferred. During this window, another\nprocess can cause a use-after-free via \u0027bpf_trampoline_link_cgroup_shim\u0027.\n\nBased on Martin KaFai Lau\u0027s suggestions, I have created a simple patch.\n\nTo fix this:\n   Add an atomic non-zero check in \u0027bpf_trampoline_link_cgroup_shim\u0027.\n   Only increment the refcount if it is not already zero.\n\nTesting:\n   I verified the fix by adding a delay in\n   \u0027bpf_shim_tramp_link_release\u0027 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-\u003etrampoline)\n\t\treturn;\n\n+\tmsleep(100);\n\tWARN_ON_ONCE(bpf_trampoline_unlink_prog(\u0026shim_link-\u003elink,\n\t\tshim_link-\u003etrampoline, NULL));\n\tbpf_trampoline_put(shim_link-\u003etrampoline);\n}\n\nBefore the patch, running a PoC easily reproduced the crash(almost 100%)\nwith a call trace similar to KaiyanM\u0027s report.\nAfter the patch, the bug no longer occurs even after millions of\niterations."
    },
    {
      "lang": "es",
      "value": "En el n\u00facleo de Linux, se ha solucionado la siguiente vulnerabilidad: bpf: Correcci\u00f3n de un problema de UAF en bpf_trampoline_link_cgroup_shim. La causa principal de este error es que, cuando \u00abbpf_link_put\u00bb reduce a cero el contador de referencias de \u00abshim_link-\u0026gt;link.link\u00bb, el recurso se considera liberado, pero a\u00fan puede ser referenciado a trav\u00e9s de \u00abtr-\u0026gt;progs_hlist\u00bb en \u00abcgroup_shim_find\u00bb. La limpieza real de \u00abtr-\u0026gt;progs_hlist\u00bb en \u00abbpf_shim_tramp_link_release\u00bb se aplaza. Durante este intervalo, otro proceso puede provocar un uso despu\u00e9s de la liberaci\u00f3n a trav\u00e9s de \u00abbpf_trampoline_link_cgroup_shim\u00bb. Bas\u00e1ndome en las sugerencias de Martin KaFai Lau, he creado un parche sencillo. Para solucionar esto: a\u00f1adir una comprobaci\u00f3n at\u00f3mica de que no sea cero en \u00abbpf_trampoline_link_cgroup_shim\u00bb. Solo incrementar el contador de referencias si a\u00fan no es cero. Pruebas: He verificado la correcci\u00f3n a\u00f1adiendo un retraso en \u00abbpf_shim_tramp_link_release\u00bb para que el error sea m\u00e1s f\u00e1cil de provocar: static void bpf_shim_tramp_link_release(struct bpf_link *link) { /* ... */ if (!shim_link-\u0026gt;trampoline) return; + msleep(100); WARN_ON_ONCE(bpf_trampoline_unlink_prog(\u0026amp;shim_link-\u0026gt;link, shim_link-\u0026gt;trampoline, NULL)); bpf_trampoline_put(shim_link-\u0026gt;trampoline); } Antes del parche, al ejecutar un PoC se reproduc\u00eda f\u00e1cilmente el bloqueo (casi al 100 %) con un seguimiento de llamadas similar al del informe de KaiyanM. Tras el parche, el error ya no se produce ni siquiera tras millones de iteraciones."
    }
  ],
  "id": "CVE-2026-23319",
  "lastModified": "2026-04-23T21:05:38.103",
  "metrics": {
    "cvssMetricV31": [
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        "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"
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        "exploitabilityScore": 1.8,
        "impactScore": 5.9,
        "source": "nvd@nist.gov",
        "type": "Primary"
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  "published": "2026-03-25T11:16:28.570",
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  "vulnStatus": "Analyzed",
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          "value": "CWE-416"
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      "source": "nvd@nist.gov",
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}


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  • 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.
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