CVE-2026-72317 (GCVE-0-2026-72317)

Vulnerability from cvelistv5 – Published: 2026-08-15 05:55 – Updated: 2026-08-17 05:42
VLAI
Title
SUNRPC: pin upper rpc_clnt across the TLS connect_worker
Summary
In the Linux kernel, the following vulnerability has been resolved: SUNRPC: pin upper rpc_clnt across the TLS connect_worker The TLS connect path has a use-after-free: nothing pins the upper rpc_clnt across the delayed connect_worker. xs_connect() stores task->tk_client in sock_xprt::clnt as a raw pointer and queues the worker; for TLS-secured transports that worker is xs_tcp_tls_setup_socket(), which reads several fields out of the saved pointer (cl_timeout, cl_program, cl_prog, cl_vers, cl_cred, cl_stats) to construct the args for the inner handshake rpc_clnt. The xprt does not reference the rpc_clnt; the rpc_clnt references the xprt. xs_destroy() does cancel the connect_worker, but it runs only when the xprt's refcount drops to zero, which cannot happen until the rpc_clnt releases its cl_xprt reference in rpc_free_client_work(). When a TLS handshake fails fatally (for example, an mTLS mount whose client cert does not match the server), the connecting task is woken with -EACCES and exits, the mount caller invokes rpc_shutdown_client(), and the upper rpc_clnt is freed before the queued connect_worker fires. xs_tcp_tls_setup_socket() then dereferences the freed clnt, producing the refcount_t underflow Michael Nemanov reported. Take a reference on the upper rpc_clnt in xs_connect() for TLS transports via a new rpc_hold_client() helper, and drop it in the connect_worker's exit path with rpc_release_client(). The xprt_lock_connect() / xprt_unlock_connect() pairing already serialises xs_connect() with xs_tcp_tls_setup_socket(), so the take and release are balanced one-for-one. The non-TLS connect worker (xs_tcp_setup_socket) never reads sock_xprt::clnt, so leave that path alone and avoid the clnt-holds-xprt-holds-clnt cycle that would otherwise prevent xprt destruction.
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 75eb6af7acdf566c68d61e98e67ee2f235201c02 , < 79cd550f8c884523b604fbfa43eb02def74d6224 (git)
Affected: 75eb6af7acdf566c68d61e98e67ee2f235201c02 , < 7a65b41b657b71d5a77861f47dd13eb4bc8e10d0 (git)
Affected: 75eb6af7acdf566c68d61e98e67ee2f235201c02 , < 5b0427ba582d143a364301f825f4e32272f06d2d (git)
Affected: 75eb6af7acdf566c68d61e98e67ee2f235201c02 , < d49f6d098ed48775b9d27a9f9c5c220fdf76f102 (git)
Affected: 75eb6af7acdf566c68d61e98e67ee2f235201c02 , < 46bc86c833956219bbfd246c1ffd832a479c5199 (git)
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Linux Linux Affected: 6.5
Unaffected: 0 , < 6.5 (semver)
Unaffected: 6.6.145 , ≤ 6.6.* (semver)
Unaffected: 6.12.97 , ≤ 6.12.* (semver)
Unaffected: 6.18.40 , ≤ 6.18.* (semver)
Unaffected: 7.1.5 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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{
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      "affected": [
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "include/linux/sunrpc/clnt.h",
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nSUNRPC: pin upper rpc_clnt across the TLS connect_worker\n\nThe TLS connect path has a use-after-free: nothing pins the\nupper rpc_clnt across the delayed connect_worker. xs_connect()\nstores task-\u003etk_client in sock_xprt::clnt as a raw pointer\nand queues the worker; for TLS-secured transports that worker\nis xs_tcp_tls_setup_socket(), which reads several fields out\nof the saved pointer (cl_timeout, cl_program, cl_prog,\ncl_vers, cl_cred, cl_stats) to construct the args for the\ninner handshake rpc_clnt.\n\nThe xprt does not reference the rpc_clnt; the rpc_clnt\nreferences the xprt. xs_destroy() does cancel the\nconnect_worker, but it runs only when the xprt\u0027s refcount\ndrops to zero, which cannot happen until the rpc_clnt\nreleases its cl_xprt reference in rpc_free_client_work().\nWhen a TLS handshake fails fatally (for example, an mTLS\nmount whose client cert does not match the server), the\nconnecting task is woken with -EACCES and exits, the mount\ncaller invokes rpc_shutdown_client(), and the upper rpc_clnt\nis freed before the queued connect_worker fires.\nxs_tcp_tls_setup_socket() then dereferences the freed clnt,\nproducing the refcount_t underflow Michael Nemanov reported.\n\nTake a reference on the upper rpc_clnt in xs_connect() for\nTLS transports via a new rpc_hold_client() helper, and drop\nit in the connect_worker\u0027s exit path with rpc_release_client().\nThe xprt_lock_connect() / xprt_unlock_connect() pairing\nalready serialises xs_connect() with xs_tcp_tls_setup_socket(),\nso the take and release are balanced one-for-one.\n\nThe non-TLS connect worker (xs_tcp_setup_socket) never reads\nsock_xprt::clnt, so leave that path alone and avoid the\nclnt-holds-xprt-holds-clnt cycle that would otherwise prevent\nxprt destruction."
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            "version": "3.1"
          },
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              "value": "AV:N - The flaw is in the SUNRPC TCP-with-TLS client connect_worker processing a remote NFS server\u0027s TLS handshake; a malicious or misconfigured server can induce fatal handshake failure over the network before the delayed worker runs, matching network-reachable kTLS/RPC-with-TLS client paths.\nAC:L - An attacker operating a reachable NFS endpoint can reliably cause fatal TLS handshake failure (e.g., reject mTLS client certificates or send TLS alerts) and influence reconnect timing/backoff so client teardown frees rpc_clnt before the queued connect_worker executes.\nPR:N - Exploitation requires no privileges on the victim host; a remote peer only needs the client kernel to initiate or re-establish an NFS RPC-with-TLS connection, and TLS handshake processing occurs before NFS authentication completes.\nUI:N - No further victim action is needed once an NFS xprtsec=tls/mtls mount exists because automatic reconnect after server-induced disconnect or handshake failure can trigger the race without additional user interaction.\nS:U - Impact is confined to kernel memory corruption and privilege boundaries within the same host; this is standard local kernel compromise rather than crossing VM, container, or IOMMU security scopes.\nC:H - This is a kernel heap use-after-free where xs_tcp_tls_setup_socket reads multiple fields from a freed rpc_clnt (including cl_cred and cl_program), enabling information disclosure and further exploitation beyond a simple crash.\nI:H - Use-after-free of rpc_clnt permits corrupting allocator metadata and adjacent kernel objects; freed-object reuse can yield arbitrary write or control-flow hijack primitives, not merely authenticated data alteration.\nA:H - Accessing the freed rpc_clnt produces a refcount_t underflow and kernel oops/panic; even unsuccessful exploitation typically crashes or hangs the system, and repeated reconnect attempts can deny availability."
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-72317",
    "datePublished": "2026-08-15T05:55:31.022Z",
    "dateReserved": "2026-08-09T03:40:39.919Z",
    "dateUpdated": "2026-08-17T05:42:43.024Z",
    "state": "PUBLISHED"
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  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • 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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  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.