{"id":"CVE-2025-39804","state":"PUBLISHED","title":"lib/crypto: arm64/poly1305: Fix register corruption in no-SIMD contexts","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nlib/crypto: arm64/poly1305: Fix register corruption in no-SIMD contexts\n\nRestore the SIMD usability check that was removed by commit a59e5468a921\n(\"crypto: arm64/poly1305 - Add block-only interface\").\n\nThis safety check is cheap and is well worth eliminating a footgun.\nWhile the Poly1305 functions should not be called when SIMD registers\nare unusable, if they are anyway, they should just do the right thing\ninstead of corrupting random tasks' registers and/or computing incorrect\nMACs.  Fixing this is also needed for poly1305_kunit to pass.\n\nJust use may_use_simd() instead of the original crypto_simd_usable(),\nsince poly1305_kunit won't rely on crypto_simd_disabled_for_test.","publishedAt":"2025-09-15T12:36:46.483Z","updatedAt":"2026-08-05T12:05:18.397Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"a59e5468a921937cb7317892779c67046ad9f5cc","status":"affected","lessThan":"ef74efa598b7bbc5c24509f7f56af2806f81c339","versionType":"git"},{"version":"a59e5468a921937cb7317892779c67046ad9f5cc","status":"affected","lessThan":"eec76ea5a7213c48529a46eed1b343e5cee3aaab","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["lib/crypto/arm64/poly1305-glue.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.16","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.16","versionType":"semver"},{"version":"6.16.4","status":"unaffected","lessThanOrEqual":"6.16.*","versionType":"semver"},{"version":"6.17","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["lib/crypto/arm64/poly1305-glue.c"]}],"references":["https://git.kernel.org/stable/c/ef74efa598b7bbc5c24509f7f56af2806f81c339","https://git.kernel.org/stable/c/eec76ea5a7213c48529a46eed1b343e5cee3aaab"],"weaknesses":[],"ingestedAt":"2026-10-29T20:09:09.358Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2025/39xxx/CVE-2025-39804.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-39804","state":"PUBLISHED","datePublished":"2025-09-15T12:36:46.483Z","dateUpdated":"2026-08-05T12:05:18.397Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2025-04-16T07:20:57.135Z"},"containers":{"cna":{"title":"lib/crypto: arm64/poly1305: Fix register corruption in no-SIMD contexts","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nlib/crypto: arm64/poly1305: Fix register corruption in no-SIMD contexts\n\nRestore the SIMD usability check that was removed by commit a59e5468a921\n(\"crypto: arm64/poly1305 - Add block-only interface\").\n\nThis safety check is cheap and is well worth eliminating a footgun.\nWhile the Poly1305 functions should not be called when SIMD registers\nare unusable, if they are anyway, they should just do the right thing\ninstead of corrupting random tasks' registers and/or computing incorrect\nMACs.  Fixing this is also needed for poly1305_kunit to pass.\n\nJust use may_use_simd() instead of the original crypto_simd_usable(),\nsince poly1305_kunit won't rely on crypto_simd_disabled_for_test."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"a59e5468a921937cb7317892779c67046ad9f5cc","status":"affected","lessThan":"ef74efa598b7bbc5c24509f7f56af2806f81c339","versionType":"git"},{"version":"a59e5468a921937cb7317892779c67046ad9f5cc","status":"affected","lessThan":"eec76ea5a7213c48529a46eed1b343e5cee3aaab","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["lib/crypto/arm64/poly1305-glue.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.16","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.16","versionType":"semver"},{"version":"6.16.4","status":"unaffected","lessThanOrEqual":"6.16.*","versionType":"semver"},{"version":"6.17","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["lib/crypto/arm64/poly1305-glue.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/ef74efa598b7bbc5c24509f7f56af2806f81c339"},{"url":"https://git.kernel.org/stable/c/eec76ea5a7213c48529a46eed1b343e5cee3aaab"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":7.5,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:N - Poly1305 is the MAC half of ChaCha20-Poly1305 and is driven directly by remote peer data in WireGuard, IPsec ESP (rfc7539esp) and kTLS on arm64 routers, phones and cloud servers, so an off-path attacker's packets are what cause the vulnerable `poly1305_blocks_arch()` invocation.\nAC:L - There is no race to win and no memory layout to groom; once the MAC computation runs in a context where SIMD is unusable the `BUG_ON(!may_use_simd())` in `kernel_neon_begin()` fires deterministically, and the attacker only has to send traffic that is MAC-verified.\nPR:N - For ChaCha20-Poly1305 AEAD the Poly1305 tag computation is itself the authentication step, so it processes an unauthenticated peer's packet before any credential is validated; no account or key on the target is needed.\nUI:N - Packet reception and the resulting AEAD tag verification happen automatically in the kernel with no action by any local user.\nS:U - The fault and its consequences are entirely within the kernel's own security authority; no VM, IOMMU or sandbox boundary is crossed.\nC:N - On arm64 the `BUG_ON` in `kernel_neon_begin()` traps before any NEON instruction executes, so the FPSIMD-register leak that the check guards against cannot be reached in the `have_neon` configuration and no memory is disclosed.\nI:N - The trap gives the attacker no write primitive, and a Poly1305 tag computed from a disturbed state fails closed on verification rather than allowing forged data to be accepted.\nA:H - Hitting `BUG_ON(!may_use_simd())` raises a kernel BUG from interrupt context, producing a fatal exception in interrupt / panic that takes down the whole system, and it can be re-triggered by simply resending traffic."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T12:05:18.397Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.16","versionEndExcluding":"6.16.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.16","versionEndExcluding":"6.17"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}