CVE-2017-9048 in libxml2
Summary
by MITRE
libxml2 20904-GITv2.9.4-16-g0741801 is vulnerable to a stack-based buffer overflow. The function xmlSnprintfElementContent in valid.c is supposed to recursively dump the element content definition into a char buffer 'buf' of size 'size'. At the end of the routine, the function may strcat two more characters without checking whether the current strlen(buf) + 2 < size. This vulnerability causes programs that use libxml2, such as PHP, to crash.
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Analysis
by VulDB Data Team • 12/18/2025
The vulnerability identified as CVE-2017-9048 represents a critical stack-based buffer overflow in libxml2 version 2.9.4, specifically within the xmlSnprintfElementContent function located in the valid.c source file. This flaw constitutes a classic buffer management error that can lead to arbitrary code execution or denial of service conditions. The affected library serves as a fundamental XML parsing component utilized by numerous applications including PHP, making this vulnerability particularly dangerous in web environments where XML processing is common. The vulnerability stems from inadequate bounds checking during string concatenation operations, creating a scenario where memory corruption can occur when processing malformed XML content.
The technical implementation of this vulnerability occurs during the recursive dumping of element content definitions into a character buffer named 'buf' with a predetermined size limit. The xmlSnprintfElementContent function performs operations that may append two additional characters to the existing buffer content without verifying whether the resulting string would exceed the allocated buffer size. This specific flaw manifests when the function calculates strlen(buf) + 2 and fails to compare this value against the buffer size parameter, creating a condition where buffer overflow occurs. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, which represents a well-documented class of memory corruption vulnerabilities that have been extensively studied in cybersecurity literature.
The operational impact of CVE-2017-9048 extends beyond simple application crashes to potentially enable remote code execution when exploited in vulnerable applications. Since libxml2 is widely used across various software platforms including web servers, content management systems, and scripting languages like PHP, a successful exploitation could compromise entire web applications or server environments. The vulnerability's exploitation requires a malicious XML payload that triggers the specific code path within the xmlSnprintfElementContent function, making it suitable for attack vectors such as XML External Entity (XXE) processing or file upload validation bypasses. This vulnerability directly maps to ATT&CK technique T1203 - Exploitation for Client Execution, where adversaries leverage software vulnerabilities to execute arbitrary code on target systems.
Mitigation strategies for CVE-2017-9048 should prioritize immediate patching of affected libxml2 installations to version 2.9.5 or later, which contains the necessary fixes for the buffer overflow condition. Organizations should implement comprehensive input validation measures that sanitize all XML content before processing, particularly when dealing with user-supplied data. Network segmentation and application firewalls can help reduce the attack surface by limiting direct access to XML processing endpoints. Additionally, implementing proper memory protection mechanisms such as stack canaries and address space layout randomization can make exploitation more difficult. Security monitoring should include detection of unusual XML processing patterns and memory allocation behaviors that might indicate exploitation attempts. The vulnerability serves as a reminder of the critical importance of proper buffer management in security-critical libraries and demonstrates how seemingly minor code flaws can result in significant security implications across the entire software ecosystem.