Re: [OE-core][PATCH v3 9/9] cve-exclusions: set status for CVE-2023-6240

[Paul Barker <paul@pbarker.dev>]

On Wed, 2026-08-12 at 02:28 -0500, Junjie Cao wrote:
> "Marvin" is Hubert Kario's Bleichenbacher-style timing oracle research:
> 
>   https://people.redhat.com/~hkario/marvin/
> 
> The affected code is the generic software RSA PKCS#1 v1.5 unpadding in
> crypto/rsa-pkcs1pad.c. pkcs1pad_decrypt_complete() has three
> secret-dependent early exits (leading zero byte, block type, minimum
> padding length) and a loop whose trip count depends on the position of
> the separator, so the time taken reveals padding validity. There is no
> constant-time unpadding or implicit-rejection fallback in the tree.
> 
> Red Hat classifies it CWE-203 and has shipped fixes only in RHEL errata
> (RHSA-2024:2758, RHSA-2024:3618 and others); the bugzilla is still NEW.
> Ubuntu records it unfixed upstream as of 2024-08-24 and Debian lists
> src:linux vulnerable in all suites:
> 
>   https://access.redhat.com/security/cve/CVE-2023-6240
>   https://ubuntu.com/security/CVE-2023-6240
>   https://security-tracker.debian.org/tracker/CVE-2023-6240
> 
> Practical exposure is narrow: kernel PKCS#1 v1.5 use is dominated by
> signature verification rather than decryption, and an attacker needs a
> service driving KEYCTL_PKEY_DECRYPT with a long-lived key. The leaky
> primitive is nevertheless reachable.

I'd drop this paragraph. Validating its claims would be time consuming.

> 
> CC: Paul Barker <paul@pbarker.dev>
> AI-Generated: Uses Claude (claude-opus-5)
> Signed-off-by: Junjie Cao <junjie.cao@linux.dev>
> ---
> v3:
> - drop the Marvell/s390 aside and the unrelated e8829ef1f73f paragraph
>   flagged in review as LLM confusion artifacts
> 
> v2: https://lore.kernel.org/openembedded-core/20260803084827.1348810-1-junjie.cao@linux.dev/
> 
>  meta/recipes-kernel/linux/cve-exclusion.inc | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/meta/recipes-kernel/linux/cve-exclusion.inc b/meta/recipes-kernel/linux/cve-exclusion.inc
> index 35e0a66..637f8b6 100644
> --- a/meta/recipes-kernel/linux/cve-exclusion.inc
> +++ b/meta/recipes-kernel/linux/cve-exclusion.inc
> @@ -252,3 +252,10 @@ affected fs/jfs txEnd()/lmLogClose() unmount race is unchanged"
>  # https://lore.kernel.org/linux-nvme/20231016060519.231880-1-joshi.k@samsung.com/
>  CVE_STATUS[CVE-2023-6238] = "unpatched: the proposed fix was applied to \
>  nvme-6.6 and then reverted, no upstream fix has landed since"
> +
> +# "Marvin": the PKCS#1 v1.5 unpadding in crypto/rsa-pkcs1pad.c branches on
> +# secret-derived data, leaking padding validity by timing. Still present in
> +# mainline; fixed only in RHEL errata.
> +# https://people.redhat.com/~hkario/marvin/
> +CVE_STATUS[CVE-2023-6240] = "unpatched: Bleichenbacher-style timing oracle in \
> +crypto/rsa-pkcs1pad.c is still present in mainline, fixed only downstream in RHEL"

Recommended wording, links and include triage date:

    # Triaged August 2026 - "Marvin" attack, Red Hat reports this fixed but the
    # exact patch is unidentified (see RHSA-2024:2758, RHSA-2024:3618 & others).
    # Unfixed in Debian, "Needs evaluation" in Ubuntu.
    # https://people.redhat.com/~hkario/marvin/
    # https://access.redhat.com/security/cve/cve-2023-6240
    # https://security-tracker.debian.org/tracker/CVE-2023-6240
    # https://ubuntu.com/security/CVE-2023-6240
    CVE_STATUS[CVE-2023-6240] = "unpatched: Fixed in RHEL but patch not identified \
    publicly"

Best regards,

-- 
Paul Barker