CVE-2026-102474 in Red Hat
Summary
by MITRE • 09/29/2026
A flaw was found in dash. The printf builtin reserves four bytes before converting a Unicode \u or \U escape, but the multi-byte token can need five or six bytes. A local user who can supply such an escape to dash printf or echo %b, including through dash -c and a positional argument, can write one or two bytes past that reservation.
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Analysis
by VulDB Data Team • 09/29/2026
The vulnerability identified in the Dash shell involves a critical buffer overflow within its built-in printf command when processing Unicode escape sequences. Specifically, the implementation allocates a fixed four-byte buffer to handle conversions for \u and \U format specifiers intended to represent wide characters or multi-byte tokens. However, certain valid UTF-8 encodings require five or six bytes to be properly represented in memory during the conversion process. This discrepancy between the allocated space and the actual data size creates an off-by-one or larger buffer overflow condition, allowing a local user who can inject such escape sequences into dash printf or echo %b commands to write one or two bytes beyond the reserved boundary.
From a technical perspective, this flaw stems from insufficient bounds checking during string manipulation operations within the shell's core utilities. When a positional argument containing these specific Unicode escapes is passed via dash -c or standard input, the parser attempts to convert the sequence without verifying if the resulting byte array fits within the pre-allocated stack buffer. This lack of dynamic size validation leads to memory corruption, which can potentially be exploited to overwrite adjacent memory structures such as return addresses or function pointers on the call stack. The impact is particularly severe in environments where scripts are executed with elevated privileges or when user-supplied input is not adequately sanitized before being passed to shell builtins.
The operational impact of this vulnerability allows for local privilege escalation if the vulnerable script runs under a higher-privileged account, such as root. An attacker could craft malicious inputs that trigger the buffer overflow to execute arbitrary code within the context of the running process. This aligns with common exploitation techniques categorized under CWE-120 Buffer Copy without Checking Size of Input and CWE-78 Improper Neutralization of Special Elements used in an OS Command, as it involves manipulating command-line arguments or script inputs to alter program execution flow. Furthermore, this type of memory corruption vulnerability is often associated with ATT&CK technique T1059 Command and Scripting Interpreter abuse, where attackers leverage system utilities like shell interpreters to achieve initial access or lateral movement within a compromised network segment.
Mitigation strategies for this issue primarily involve updating the Dash package to a version that includes patches addressing these buffer allocation checks. System administrators should ensure that all instances of Dash are updated through their respective operating system repositories, as vendors typically release security advisories and patched binaries promptly after such vulnerabilities are disclosed. In addition to software updates, defensive coding practices within custom shell scripts can reduce risk by avoiding the direct use of user-supplied data in printf or echo %b commands without prior validation. Input sanitization techniques that restrict allowed characters or validate expected formats before passing them to these builtins can serve as an effective compensating control until patches are applied. Organizations should also monitor for unusual process behavior originating from shell scripts, particularly those involving unexpected memory access patterns or privilege changes, using endpoint detection and response tools configured to flag potential exploitation attempts of known buffer overflow vulnerabilities in system utilities.