Developers have submitted patches to the Linux kernel to eliminate support for the insecure SHA-1 hashing algorithm in signing kernel modules. This move addresses known vulnerabilities like collision attacks demonstrated in 2017. The changes build on prior efforts to enhance kernel security.
The Linux kernel community is advancing security by proposing patches to phase out SHA-1 support for signing kernel modules. Petr Pavlu, the patch author, posted the series to the Linux kernel mailing list this week, as reported by Phoronix. Pavlu stated: “SHA-1 is considered deprecated and insecure due to vulnerabilities that can lead to hash collisions.”
This initiative follows years of warnings about SHA-1's weaknesses, particularly after researchers showed practical collision attacks in 2017. A previous attempt to remove SHA-1 support via commit 16ab7cb5825f was reverted due to compatibility issues with tools like iwd. Last year, the default signing algorithm shifted to SHA-512 in commit f3b93547b91a without major problems, setting the stage for full deprecation.
The patches consist of two main changes. The first modifies the kernel's module Kconfig to remove SHA-1 options, referencing the earlier reverted commit. The second targets the sign-file utility, eliminating PKCS#7 support, which was limited to SHA-1. James Bottomley clarified in a mailing list response: “CMS really is PKCS7 and most literature will refer to CMS as PKCS7,” noting that the update deprecates an outdated API.
Most major Linux distributions have already adopted SHA-2 for module signing. However, Android lags, using SHA-1 by default for its Generic Kernel Image (GKI). Sami noted on the mailing list: “Overall, Android doesn’t rely on module signing for security, it’s only used to differentiate between module types.” The patches focus on dropping SHA-1 for new signatures while allowing existing ones to load.
Implementation faces minor hurdles, including a conflict with an ongoing series for ML-DSA support. Pavlu acknowledged: “The second patch has a minor conflict with the sign-file update in the series ‘lib/crypto: Add ML-DSA’.” Community reactions on platforms like X have been positive, with Phoronix announcing: “Linux Looks To Remove SHA1 Support For Signing Kernel Modules. Time to move to more secure hashing algorithms.” These changes aim to bolster security in environments like servers and embedded systems by reducing risks of forged signatures.