CVE-2011-4357 in Clearsilver
Summary
by MITRE
Format string vulnerability in the p_cgi_error function in python/neo_cgi.c in the Python CGI Kit (neo_cgi) module for Clearsilver 0.10.5 and earlier allows remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via format string specifiers that are not properly handled when creating CGI error messages using the cgi_error API function.
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Analysis
by VulDB Data Team • 11/28/2021
The vulnerability identified as CVE-2011-4357 represents a critical format string flaw within the Python CGI Kit's Clearsilver 0.10.5 and earlier versions. This issue specifically targets the p_cgi_error function located in the python/neo_cgi.c source file, which serves as the core component responsible for generating CGI error messages through the cgi_error API function. The flaw arises from improper handling of format string specifiers during error message construction, creating a pathway for malicious input to be interpreted as format specifiers rather than literal text.
The technical exploitation of this vulnerability occurs when the p_cgi_error function processes error messages without proper sanitization of input parameters that may contain format string specifiers such as %s, %d, or other conversion specifications. When these unvalidated inputs are directly passed to printf-style functions, attackers can manipulate the execution flow by injecting format specifiers that reference arbitrary memory locations or cause stack corruption. This fundamental flaw in input validation and string handling creates opportunities for both denial of service attacks through application crashes and potential arbitrary code execution.
From an operational impact perspective, this vulnerability poses significant risks to web applications utilizing Clearsilver 0.10.5 or earlier versions in their Python CGI implementations. Remote attackers can leverage this weakness to crash web servers or potentially execute malicious code on the target system with the privileges of the web server process. The vulnerability's classification as a format string vulnerability aligns with CWE-134, which specifically addresses the use of format strings with user-controlled data, making it a well-documented and dangerous class of vulnerability in software security. The potential for remote code execution through this vector makes it particularly attractive to attackers seeking persistent access to compromised systems.
The mitigation strategy for CVE-2011-4357 requires immediate remediation through upgrading to Clearsilver version 0.10.6 or later, where the format string handling has been properly addressed. Organizations should also implement proper input validation and sanitization measures for all user-supplied data that may be used in error message generation, ensuring that format string specifiers are either escaped or properly handled through safe string formatting functions. Additionally, implementing proper access controls and network segmentation can limit the potential impact of exploitation attempts, while monitoring for unusual error message patterns may help detect exploitation attempts. This vulnerability demonstrates the critical importance of proper input validation and secure coding practices in web application development, particularly when dealing with user-controllable data in error handling contexts. The ATT&CK framework categorizes this type of vulnerability under privilege escalation and code execution techniques, emphasizing the need for comprehensive security measures in web application environments.