CVE-2017-13089 in wget
Summary
by MITRE
The http.c:skip_short_body() function is called in some circumstances, such as when processing redirects. When the response is sent chunked in wget before 1.19.2, the chunk parser uses strtol() to read each chunk's length, but doesn't check that the chunk length is a non-negative number. The code then tries to skip the chunk in pieces of 512 bytes by using the MIN() macro, but ends up passing the negative chunk length to connect.c:fd_read(). As fd_read() takes an int argument, the high 32 bits of the chunk length are discarded, leaving fd_read() with a completely attacker controlled length argument.
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Analysis
by VulDB Data Team • 01/04/2023
The vulnerability identified as CVE-2017-13089 resides within the wget utility's handling of HTTP response bodies, specifically in the http.c module's skip_short_body() function. This flaw manifests during HTTP redirect processing where wget encounters chunked transfer encoded responses. The vulnerability stems from improper validation of chunk length values during the parsing process, creating a potential for arbitrary code execution or denial of service attacks. The issue affects wget versions prior to 1.19.2, making it a significant concern for systems relying on older wget installations for web content retrieval operations.
The technical root cause involves the chunked transfer encoding parser within wget's HTTP implementation. When processing chunked responses, the code utilizes strtol() to convert chunk length strings into numeric values without validating that these values represent non-negative integers. This validation gap allows malicious HTTP responses to contain negative chunk length values that bypass normal input sanitization checks. The subsequent processing of these values through the MIN() macro and ultimately to fd_read() function creates a critical path where attacker-controlled negative values can be converted to large positive integers due to integer truncation behavior in the 32-bit signed integer argument handling.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to potentially enable remote code execution or data corruption. When fd_read() receives what appears to be a large positive integer due to the truncation of negative values, it attempts to read an enormous amount of data from network connections, leading to resource exhaustion, memory corruption, or unexpected program behavior. This vulnerability aligns with CWE-191, Integer Underflow (Wrap or Wraparound), and CWE-190, Integer Overflow or Wraparound, as the negative values are processed through integer arithmetic operations that result in unintended large positive values. The attack surface is particularly concerning given wget's widespread use in automated systems, package managers, and network operations where it may process untrusted HTTP responses without proper validation.
Mitigation strategies should focus on upgrading to wget version 1.19.2 or later where the fix has been implemented. The patch addresses the issue by adding proper validation of chunk length values to ensure they are non-negative before processing, preventing negative values from reaching the fd_read() function. Organizations should also implement network segmentation and proxy configurations that can filter or validate chunked transfer encoding responses before they reach wget clients. Additional defensive measures include monitoring for unusual memory consumption patterns or network traffic spikes that might indicate exploitation attempts. This vulnerability demonstrates the importance of input validation in network protocols and aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter: Python, as the vulnerability could potentially be exploited through malicious HTTP responses that trigger command execution or resource exhaustion scenarios. The fix implementation follows security best practices by ensuring integer overflow protection and proper bounds checking in critical network processing functions, preventing the exploitation of integer arithmetic vulnerabilities that could compromise system integrity.