CVE-2018-16646 in Poppler
Summary
by MITRE
In Poppler 0.68.0, the Parser::getObj() function in Parser.cc may cause infinite recursion via a crafted file. A remote attacker can leverage this for a DoS attack.
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Analysis
by VulDB Data Team • 05/26/2020
The vulnerability identified as CVE-2018-16646 represents a critical denial of service flaw within the Poppler PDF library version 0.68.0. This issue manifests through the Parser::getObj() function located in the Parser.cc source file, where a specially crafted PDF document can trigger infinite recursive calls that ultimately lead to system resource exhaustion and application crash. The flaw demonstrates characteristics consistent with a stack overflow condition that occurs during recursive parsing operations when processing malformed input files, making it particularly dangerous in environments where PDF documents are automatically processed or rendered without proper validation.
The technical implementation of this vulnerability stems from insufficient input validation within the PDF parsing logic of Poppler. When the Parser::getObj() function encounters a malformed PDF structure containing recursive references or circular data patterns, it fails to implement proper recursion depth limits or termination conditions. This allows an attacker to construct a PDF file that contains nested objects or references that cause the parser to repeatedly call itself without reaching a base case condition. The recursive nature of the flaw means that each function call consumes stack space, and without proper bounds checking, the stack can overflow rapidly, leading to process termination or system instability.
From an operational perspective, this vulnerability poses significant risks to any system that processes PDF documents automatically, including web applications, email servers, document management systems, and security scanning tools. Remote attackers can exploit this weakness by simply delivering a malicious PDF file to a vulnerable system, requiring no special privileges or complex attack vectors. The impact extends beyond simple service disruption as the DoS condition can be sustained, potentially allowing attackers to consume system resources indefinitely or cause cascading failures in applications that depend on Poppler for PDF processing. This vulnerability directly maps to CWE-674, which describes "Uncontrolled Recursion" in software systems, and aligns with ATT&CK technique T1499.004 for Network Denial of Service, making it a particularly concerning threat in enterprise environments where PDF processing is a common operational requirement.
Mitigation strategies for CVE-2018-16646 should prioritize immediate patching of affected Poppler installations to version 0.69.0 or later, where the recursive parsing logic has been corrected with proper depth limiting mechanisms. Organizations should also implement input validation measures such as PDF file sanitization, content filtering, and sandboxed processing environments that can contain potential exploitation attempts. Network-level protections including PDF content inspection and blocking of suspicious file types can provide additional layers of defense. Security teams should monitor for exploitation attempts through log analysis and implement proper resource limits on PDF processing services to prevent complete system exhaustion even if a vulnerability is exploited. The fix implemented in later Poppler versions typically includes stack depth monitoring and early termination of recursive parsing operations when predefined limits are exceeded, addressing the core issue that allowed unbounded recursion to occur.