{"cve":"CVE-2023-53024","nvd":{"published":"2025-03-27T17:15:51.980","modified":"2026-06-17T06:44:08.850","status":"Analyzed","description":"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 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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H","score":7.1},"cwes":[],"references":["https://git.kernel.org/stable/c/01bdcc73dbe7be3ad4d4ee9a59b71e42f461a528","https://git.kernel.org/stable/c/81b3374944d201872cfcf82730a7860f8e7c31dd","https://git.kernel.org/stable/c/aae109414a57ab4164218f36e2e4a17f027fcaaa","https://git.kernel.org/stable/c/b0c89ef025562161242a7c19b213bd6b272e93df","https://git.kernel.org/stable/c/da75dec7c6617bddad418159ffebcb133f008262"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:00:28.034033815+00:00"},"epss":{"cve":"CVE-2023-53024","score":0.00206,"percentile":0.10625,"date":"2026-11-01"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}