CVE-2021-47107
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk31th percentile - higher than 31% of all known CVEs
Summary
A vulnerability related to buffer overflow in the READDIR function has been identified in the Linux kernel. The issue occurs when a client sends a count argument that is too small, leading to incorrect buffer size calculations and allowing writes beyond its boundaries.
Risk Assessment
This vulnerability could lead to unauthorized memory access, posing risks to data integrity and confidentiality within the system. An attacker could exploit this flaw to inject malicious code or destabilize the system.
Recommendation
It is recommended to update the Linux kernel to the latest version that includes fixes for this vulnerability. Additionally, implementing argument validation mechanisms in applications using NFSD is advisable.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: NFSD: Fix READDIR buffer overflow If a client sends a READDIR count argument that is too small (say, zero), then the buffer size calculation in the new init_dirlist helper functions results in an underflow, allowing the XDR stream functions to write beyond the actual buffer. This calculation has always been suspect. NFSD has never sanity- checked the READDIR count argument, but the old entry encoders managed the problem correctly. With the commits below, entry encoding changed, exposing the underflow to the pointer arithmetic in xdr_reserve_space(). Modern NFS clients attempt to retrieve as much data as possible for each READDIR request. Also, we have no unit tests that exercise the behavior of READDIR at the lower bound of @count values. Thus this case was missed during testing.