CVE-2025-21646

Name of the Vulnerable Software and Affected Versions Linux kernel versions prior to 6.6.74

Description The issue arises in the kafs filesystem, which limits the maximum length of a cell to 256 bytes. However, when this limit is reached, kafs attempts to create a directory under /proc/net/afs/ with the cell name, resulting in a warning due to procfs's 255-byte filename limit. The DNS also limits the maximum lookup length, and consequently, the maximum cell name, to 253 bytes. To resolve this, the maximum acceptable cell name length is limited to 253 bytes, ensuring the creation of the /afs/.<cell>/ mountpoint. The YFS VL record cell name maximum is split to 256 bytes as allowed by the protocol, and records exceeding 253 bytes retrieved by YFSVL.GetCellName are ignored.

Recommendations For Linux kernel versions prior to 6.6.74, update to version 6.6.74 or later to resolve the issue. As a temporary workaround, consider limiting the cell name length to 253 bytes to prevent warnings and ensure the creation of the /afs/.<cell>/ mountpoint. Restrict access to the YFSVL.GetCellName function to minimize the risk of exploitation until the issue is resolved.