CWE-134 (使用外部控制的格式字符串) — Vulnerability Class 151

151 vulnerabilities classified as CWE-134 (使用外部控制的格式字符串). AI Chinese analysis included.

CWE-134 represents a critical input validation weakness where software utilizes functions accepting format strings, such as printf, with data originating from an untrusted external source. Attackers typically exploit this vulnerability by injecting malicious format specifiers, like %x or %n, into the input stream. This manipulation allows them to read sensitive memory contents, causing denial of service, or write arbitrary data to memory, potentially leading to remote code execution and full system compromise. To mitigate this risk, developers must strictly avoid passing user-controlled data directly as the format string argument. Instead, they should use literal format strings and pass user input as subsequent arguments. Additionally, implementing rigorous input validation and employing static analysis tools can help detect these dangerous patterns early in the development lifecycle, ensuring that external data is never interpreted as executable code logic.

MITRE CWE Description

The product uses a function that accepts a format string as an argument, but the format string originates from an external source.

Common Consequences (2)

Confidentiality Read Memory

Format string problems allow for information disclosure which can severely simplify exploitation of the program.

Integrity, Confidentiality, Availability Modify Memory, Execute Unauthorized Code or Commands

Format string problems can result in the execution of arbitrary code, buffer overflows, denial of service, or incorrect data representation.

Mitigations (3)

Requirements Choose a language that is not subject to this flaw.

Implementation Ensure that all format string functions are passed a static string which cannot be controlled by the user, and that the proper number of arguments are always sent to that function as well. If at all possible, use functions that do not support the %n operator in format strings. [REF-116] [REF-117]

Build and Compilation Run compilers and linkers with high warning levels, since they may detect incorrect usage.

Examples (2)

The following program prints a string provided as an argument.

#include <stdio.h> void printWrapper(char *string) { printf(string); } int main(int argc, char **argv) { char buf[5012]; memcpy(buf, argv[1], 5012); printWrapper(argv[1]); return (0); }

Bad · C

The following code copies a command line argument into a buffer using snprintf().

int main(int argc, char **argv){ char buf[128]; ... snprintf(buf,128,argv[1]); }

Bad · C

CVE ID	Title	CVSS	Severity	Published
CVE-2017-3859	Cisco ASR 920 Series Aggregation Services Routers Zero Touch Provisioning 安全漏洞 — Cisco IOS XE Software for Cisco ASR 920 Series Routers	8.6	-	2017-03-22

Vulnerabilities classified as CWE-134 (使用外部控制的格式字符串) represent 151 CVEs. The CWE taxonomy describes the weakness; review individual CVEs for product-specific impact.