Vulnerabilities > CVE-2021-47107 - Classic Buffer Overflow vulnerability in Linux Kernel
Summary
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.
Vulnerable Configurations
Common Weakness Enumeration (CWE)
Common Attack Pattern Enumeration and Classification (CAPEC)
- Buffer Overflow via Environment Variables This attack pattern involves causing a buffer overflow through manipulation of environment variables. Once the attacker finds that they can modify an environment variable, they may try to overflow associated buffers. This attack leverages implicit trust often placed in environment variables.
- Overflow Buffers Buffer Overflow attacks target improper or missing bounds checking on buffer operations, typically triggered by input injected by an attacker. As a consequence, an attacker is able to write past the boundaries of allocated buffer regions in memory, causing a program crash or potentially redirection of execution as per the attackers' choice.
- Client-side Injection-induced Buffer Overflow This type of attack exploits a buffer overflow vulnerability in targeted client software through injection of malicious content from a custom-built hostile service.
- Filter Failure through Buffer Overflow In this attack, the idea is to cause an active filter to fail by causing an oversized transaction. An attacker may try to feed overly long input strings to the program in an attempt to overwhelm the filter (by causing a buffer overflow) and hoping that the filter does not fail securely (i.e. the user input is let into the system unfiltered).
- MIME Conversion An attacker exploits a weakness in the MIME conversion routine to cause a buffer overflow and gain control over the mail server machine. The MIME system is designed to allow various different information formats to be interpreted and sent via e-mail. Attack points exist when data are converted to MIME compatible format and back.
References
- https://git.kernel.org/stable/c/53b1119a6e5028b125f431a0116ba73510d82a72
- https://git.kernel.org/stable/c/53b1119a6e5028b125f431a0116ba73510d82a72
- https://git.kernel.org/stable/c/9e291a6a28d32545ed2fd959a8165144d1724df1
- https://git.kernel.org/stable/c/9e291a6a28d32545ed2fd959a8165144d1724df1
- https://git.kernel.org/stable/c/eabc0aab98e5218ceecd82069b0d6fdfff5ee885
- https://git.kernel.org/stable/c/eabc0aab98e5218ceecd82069b0d6fdfff5ee885