{"id":"CVE-2023-53024","title":"bpf: Fix pointer-leak due to insufficient speculative store bypass mitigation","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix pointer-leak due to insufficient speculative store bypass mitigation\n\nTo mitigate Spectre v4, 2039f26f3aca (\"bpf: Fix leakage due to\ninsufficient speculative s…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 872968502114d68c21419cf7eb5ab97717e7b803 < aae109414a57ab4164218f36e2e4a17f027fcaaa","Linux >= f5893af2704eb763eb982f01d573f5b19f06b623 < 81b3374944d201872cfcf82730a7860f8e7c31dd","Linux >= 0e9280654aa482088ee6ef3deadef331f5ac5fb0 < da75dec7c6617bddad418159ffebcb133f008262","Linux >= 2039f26f3aca5b0e419b98f65dd36481337b86ee < 01bdcc73dbe7be3ad4d4ee9a59b71e42f461a528","Linux >= 2039f26f3aca5b0e419b98f65dd36481337b86ee < b0c89ef025562161242a7c19b213bd6b272e93df","Linux >= 2039f26f3aca5b0e419b98f65dd36481337b86ee < e4f4db47794c9f474b184ee1418f42e6a07412b6","Linux 0b27bdf02c400684225ee5ee99970bcbf5082282","Linux >= 4.19.207 < 4.19.272","Linux >= 5.4.146 < 5.4.231","Linux >= 5.10.56 < 5.10.166","Linux >= 5.13.8 < 5.14","Linux 5.14"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-11-05T20:14:43.758869Z"},"published":"2025-03-27","updated":"2026-11-05","sourceUpdated":"2026-11-05T20:20:54.663Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2023-53024","references":[{"url":"https://git.kernel.org/stable/c/aae109414a57ab4164218f36e2e4a17f027fcaaa"},{"url":"https://git.kernel.org/stable/c/81b3374944d201872cfcf82730a7860f8e7c31dd"},{"url":"https://git.kernel.org/stable/c/da75dec7c6617bddad418159ffebcb133f008262"},{"url":"https://git.kernel.org/stable/c/01bdcc73dbe7be3ad4d4ee9a59b71e42f461a528"},{"url":"https://git.kernel.org/stable/c/b0c89ef025562161242a7c19b213bd6b272e93df"},{"url":"https://git.kernel.org/stable/c/e4f4db47794c9f474b184ee1418f42e6a07412b6"}],"tags":["cve.org"],"epss":0.00206,"epssPercentile":0.10658,"ingestedAt":"2026-11-05T22:38:31.761Z","slug":"CVE-2023-53024","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix pointer-leak due to insufficient speculative store bypass mitigation\n\nTo mitigate Spectre v4, 2039f26f3aca (\"bpf: Fix leakage due to\ninsufficient speculative store bypass mitigation\") inserts lfence\ninstructions after 1) initializing a stack slot and 2) spilling a\npointer to the stack.\n\nHowever, this does not cover cases where a stack slot is first\ninitialized with a pointer (subject to sanitization) but then\noverwritten with a scalar (not subject to sanitization because\nthe slot was already initialized). In this case, the second write\nmay be subject to speculative store bypass (SSB) creating a\nspeculative pointer-as-scalar type confusion. This allows the\nprogram to subsequently leak the numerical pointer value using,\nfor example, a branch-based cache side channel.\n\nTo fix this, also sanitize scalars if they write a stack slot\nthat previously contained a pointer. Assuming that pointer-spills\nare only generated by LLVM on register-pressure, the performance\nimpact on most real-world BPF programs should be small.\n\nThe following unprivileged BPF bytecode drafts a minimal exploit\nand the mitigation:\n\n  [...]\n  // r6 = 0 or 1 (skalar, unknown user input)\n  // r7 = accessible ptr for side channel\n  // r10 = frame pointer (fp), to be leaked\n  //\n  r9 = r10 # fp alias to encourage ssb\n  *(u64 *)(r9 - 8) = r10 // fp[-8] = ptr, to be leaked\n  // lfence added here because of pointer spill to stack.\n  //\n  // Ommitted: Dummy bpf_ringbuf_output() here to train alias predictor\n  // for no r9-r10 dependency.\n  //\n  *(u64 *)(r10 - 8) = r6 // fp[-8] = scalar, overwrites ptr\n  // 2039f26f3aca: no lfence added because stack slot was not STACK_INVALID,\n  // store may be subject to SSB\n  //\n  // fix: also add an lfence when the slot contained a ptr\n  //\n  r8 = *(u64 *)(r9 - 8)\n  // r8 = architecturally a scalar, speculatively a ptr\n  //\n  // leak ptr using branch-based cache side channel:\n  r8 &= 1 // choose bit to leak\n  if r8 == 0 goto SLOW // no mispredict\n  // architecturally dead code if input r6 is 0,\n  // only executes speculatively iff ptr bit is 1\n  r8 = *(u64 *)(r7 + 0) # encode bit in cache (0: slow, 1: fast)\nSLOW:\n  [...]\n\nAfter running this, the program can time the access to *(r7 + 0) to\ndetermine whether the chosen pointer bit was 0 or 1. Repeat this 64\ntimes to recover the whole address on amd64.\n\nIn summary, sanitization can only be skipped if one scalar is\noverwritten with another scalar. Scalar-confusion due to speculative\nstore bypass can not lead to invalid accesses because the pointer\nbounds deducted during verification are enforced using branchless\nlogic. See 979d63d50c0c (\"bpf: prevent out of bounds speculation on\npointer arithmetic\") for details.\n\nDo not make the mitigation depend on !env->allow_{uninit_stack,ptr_leaks}\nbecause speculative leaks are likely unexpected if these were enabled.\nFor example, leaking the address to a protected log file may be acceptable\nwhile disabling the mitigation might unintentionally leak the address\ninto the cached-state of a map that is accessible to unprivileged\nprocesses.\n\n## Affected\n\n- `Linux >= 872968502114d68c21419cf7eb5ab97717e7b803 < aae109414a57ab4164218f36e2e4a17f027fcaaa`\n- `Linux >= f5893af2704eb763eb982f01d573f5b19f06b623 < 81b3374944d201872cfcf82730a7860f8e7c31dd`\n- `Linux >= 0e9280654aa482088ee6ef3deadef331f5ac5fb0 < da75dec7c6617bddad418159ffebcb133f008262`\n- `Linux >= 2039f26f3aca5b0e419b98f65dd36481337b86ee < 01bdcc73dbe7be3ad4d4ee9a59b71e42f461a528`\n- `Linux >= 2039f26f3aca5b0e419b98f65dd36481337b86ee < b0c89ef025562161242a7c19b213bd6b272e93df`\n- `Linux >= 2039f26f3aca5b0e419b98f65dd36481337b86ee < e4f4db47794c9f474b184ee1418f42e6a07412b6`\n- `Linux 0b27bdf02c400684225ee5ee99970bcbf5082282`\n- `Linux >= 4.19.207 < 4.19.272`\n- `Linux >= 5.4.146 < 5.4.231`\n- `Linux >= 5.10.56 < 5.10.166`\n- `Linux >= 5.13.8 < 5.14`\n- `Linux 5.14`\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":[]}