CVE-2025-39804 (GCVE-0-2025-39804)

Vulnerability from cvelistv5 – Published: 2025-09-15 12:36 – Updated: 2026-08-05 12:05
VLAI
Title
lib/crypto: arm64/poly1305: Fix register corruption in no-SIMD contexts
Summary
In the Linux kernel, the following vulnerability has been resolved: lib/crypto: arm64/poly1305: Fix register corruption in no-SIMD contexts Restore the SIMD usability check that was removed by commit a59e5468a921 ("crypto: arm64/poly1305 - Add block-only interface"). This safety check is cheap and is well worth eliminating a footgun. While the Poly1305 functions should not be called when SIMD registers are unusable, if they are anyway, they should just do the right thing instead of corrupting random tasks' registers and/or computing incorrect MACs. Fixing this is also needed for poly1305_kunit to pass. Just use may_use_simd() instead of the original crypto_simd_usable(), since poly1305_kunit won't rely on crypto_simd_disabled_for_test.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: a59e5468a921937cb7317892779c67046ad9f5cc , < ef74efa598b7bbc5c24509f7f56af2806f81c339 (git)
Affected: a59e5468a921937cb7317892779c67046ad9f5cc , < eec76ea5a7213c48529a46eed1b343e5cee3aaab (git)
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Linux Linux Affected: 6.16
Unaffected: 0 , < 6.16 (semver)
Unaffected: 6.16.4 , ≤ 6.16.* (semver)
Unaffected: 6.17 , ≤ * (original_commit_for_fix)
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              "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\u0027s 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\u0027s 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\u0027s 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."
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    "redhat_vex": {
      "aggregate_severity": "None",
      "current_release_date": "2026-06-30T10:23:35+00:00",
      "cve": "CVE-2025-39804",
      "id": "CVE-2025-39804",
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      "product_status:known_not_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: lib/crypto: arm64/poly1305: Fix register corruption in no-SIMD contexts",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-39804.json",
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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.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • 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.