CVE-2026-38636 in Relibc
Summary
by MITRE • 08/28/2026
An issue in the seekdir() function (/dirent/mod.rs) of relibc commit 61f42d allows attackers to cause a Denial of Service (DoS) via a crafted input.
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Analysis
by VulDB Data Team • 08/28/2026
The vulnerability identified within the seekdir function located in the dirent module of the relibc library, specifically associated with commit 61f42d, represents a critical reliability flaw that can be exploited to induce a Denial of Service condition. This issue stems from insufficient validation or improper handling of input parameters passed to the directory stream manipulation routine. In systems programming contexts such as those handled by C-like libraries including relibc, functions like seekdir are responsible for repositioning the file descriptor associated with an open directory stream to a specific location within that directory's entry list. When this function receives crafted or malformed input, it fails to adequately check boundary conditions or state integrity before proceeding with memory operations or pointer arithmetic.
From a technical perspective, the core flaw lies in the lack of robust error handling and bounds checking when processing the offset provided by the caller. If an attacker supplies a value that is outside the valid range for the current directory stream's internal buffer structure, the function may attempt to access invalid memory addresses or enter an infinite loop while attempting to resolve the position. This behavior disrupts the normal execution flow of the application utilizing relibc. Since seekdir is often used in loops that iterate through directory entries, a failure here can cause the entire process to hang, crash, or consume excessive CPU resources as it attempts to recover from or respond to the invalid state. The absence of proper safeguards means that any untrusted data reaching this function directly compromises system stability.
The operational impact of this vulnerability is primarily centered on service availability and resource exhaustion. An attacker who can control the input parameters passed to seekdir, perhaps through a vulnerable application layer that interacts with file systems using relibc, can trigger a denial of service against the hosting process or potentially the underlying operating system if the crash propagates up the stack. This is particularly dangerous in server environments where directory listing operations are common and often exposed via network services. The inability to reliably seek within directories undermines data integrity checks that rely on consistent traversal order and prevents applications from functioning correctly, leading to potential downtime for critical infrastructure relying on this library.
This vulnerability aligns with CWE-20 Improper Input Validation, as the root cause is the failure to properly sanitize or validate user-supplied input before processing it within a system-level function. Furthermore, in terms of attack vectors and tactics, this flaw can be leveraged under ATT&CK technique T1499 Endpoint Denial of Service, where an adversary aims to disrupt the availability of specific services by exhausting resources or causing crashes through malformed inputs. The exploitation does not necessarily require privilege escalation but relies on the ability to inject malicious parameters into directory handling routines within a privileged context if relibc is used in such environments.
Mitigation strategies must focus on hardening the input validation logic within the seekdir implementation. Developers should implement strict range checking for offset values, ensuring they fall within the bounds of the currently open directory stream's valid entries. Additionally, adding defensive programming practices such as null pointer checks and state verification before performing any memory operations is essential. Updating to a patched version of relibc that addresses commit 61f42d is the primary remediation step for existing deployments. For developers integrating this library, it is crucial to ensure that all inputs originating from untrusted sources are validated at the application layer before being passed down to system calls or low-level C functions like seekdir. Regular security audits of file handling code and static analysis tools configured to detect buffer overflows and invalid memory accesses can further reduce the risk of similar vulnerabilities in related modules.