CVE-2025-38528 (GCVE-0-2025-38528)
Vulnerability from cvelistv5
Published
2025-08-16 11:12
Modified
2026-08-05 12:02
Severity ?
7.1 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: bpf: Reject %p% format string in bprintf-like helpers static const char fmt[] = "%p%"; bpf_trace_printk(fmt, sizeof(fmt)); The above BPF program isn't rejected and causes a kernel warning at runtime: Please remove unsupported %\x00 in format string WARNING: CPU: 1 PID: 7244 at lib/vsprintf.c:2680 format_decode+0x49c/0x5d0 This happens because bpf_bprintf_prepare skips over the second %, detected as punctuation, while processing %p. This patch fixes it by not skipping over punctuation. %\x00 is then processed in the next iteration and rejected.
References
Impacted products
Vendor Product Version
Linux Linux Version: 48cac3f4a96ddf08df8e53809ed066de0dc93915
Version: 48cac3f4a96ddf08df8e53809ed066de0dc93915
Version: 48cac3f4a96ddf08df8e53809ed066de0dc93915
Version: 48cac3f4a96ddf08df8e53809ed066de0dc93915
Version: 48cac3f4a96ddf08df8e53809ed066de0dc93915
Version: 48cac3f4a96ddf08df8e53809ed066de0dc93915
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Reject %p% format string in bprintf-like helpers\n\nstatic const char fmt[] = \"%p%\";\n    bpf_trace_printk(fmt, sizeof(fmt));\n\nThe above BPF program isn\u0027t rejected and causes a kernel warning at\nruntime:\n\n    Please remove unsupported %\\x00 in format string\n    WARNING: CPU: 1 PID: 7244 at lib/vsprintf.c:2680 format_decode+0x49c/0x5d0\n\nThis happens because bpf_bprintf_prepare skips over the second %,\ndetected as punctuation, while processing %p. This patch fixes it by\nnot skipping over punctuation. %\\x00 is then processed in the next\niteration and rejected."
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              "value": "AV:L - The only trigger is a locally loaded eBPF program invoking a bprintf-like helper (`bpf_trace_printk`, `bpf_trace_vprintk`, `bpf_snprintf`, `bpf_seq_printf`) via the `bpf()` syscall; the format string is attacker-authored at `BPF_PROG_LOAD` time and consumed in the calling task\u0027s own context. No remote peer or packet can supply a format string.\nAC:L - The attacker fully controls the constant format string, so `\"%p%\"` deterministically reaches the `WARN_ONCE` in `format_decode()` and `\"%p%s\"` deterministically desyncs `bpf_bprintf_prepare()` from `bstr_printf()` on the first call \u2014 no race, no timing window, no dependence on memory layout the attacker cannot influence.\nPR:L - Reaching the helpers requires CAP_BPF plus CAP_PERFMON (or CAP_SYS_ADMIN) rather than full root, and these are routinely granted to non-root eBPF observability/profiling service accounts and can be delegated into a user namespace via a BPF token (supported in all affected 6.9+ branches), so a low-privilege non-root actor suffices.\nUI:N - The attacker performs self-contained `bpf(BPF_PROG_LOAD)` and program-run/attach operations; no victim must mount a filesystem, open a file, or take any other action.\nS:U - The faulty parse, the warning, and the stale-memory read all occur in the kernel\u0027s own security authority within the calling task\u0027s context; no hypervisor, IOMMU, or sandbox boundary is crossed.\nC:H - The prepare/print desync makes `bstr_printf()`\u0027s `FORMAT_STATE_STR` `strlen()` and copy uninitialized bytes from the per-CPU `bpf_bprintf_buffers` (512-byte `bin_args` followed by the 1024-byte `buf`, and potentially past the struct into adjacent per-CPU memory) straight into the `bpf_snprintf` output buffer or trace ring buffer that the attacker reads; because `nocopy_fmt` stores raw unhashed 64-bit values there, this leaks unsanitized kernel pointers, on top of the KASLR-defeating backtrace the `WARN_ONCE` dumps to dmesg.\nI:N - All writes stay bounded \u2014 `nocopy_fmt` checks `tmp_buf_end - tmp_buf` before storing, and `bstr_printf()`/`string()` gate every store on `str \u003c end` \u2014 so the bug under-fills the argument buffer rather than overflowing it; no kernel or user memory is modified out of bounds.\nA:H - `\"%p%\"` triggers `WARN_ONCE` at `lib/vsprintf.c:2807`, which becomes a full kernel panic on the widely deployed `panic_on_warn=1` used in hardened cloud, Android, and fuzzing configurations \u2014 exactly the crash syzbot reported \u2014 and the unbounded `strlen()` over per-CPU memory can additionally fault; even without `panic_on_warn` the splat taints the kernel and can trip health-check tooling into taking the node down."
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          "url": "https://git.kernel.org/stable/c/97303e541e12f1fea97834ec64b98991e8775f39"
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          "url": "https://git.kernel.org/stable/c/61d5fa45ed13e42af14c7e959baba9908b8ee6d4"
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          "url": "https://git.kernel.org/stable/c/e7be679124bae8cf4fa6e40d7e1661baddfb3289"
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    "dateReserved": "2025-04-16T04:51:24.023Z",
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