CVE-2020-27778 in Poppler
Summary
by MITRE • 12/03/2020
A flaw was found in Poppler in the way certain PDF files were converted into HTML. A remote attacker could exploit this flaw by providing a malicious PDF file that, when processed by the 'pdftohtml' program, would crash the application causing a denial of service.
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Analysis
by VulDB Data Team • 12/12/2020
The vulnerability identified as CVE-2020-27778 represents a critical denial of service flaw within the Poppler PDF library ecosystem, specifically affecting the pdftohtml conversion utility. This issue stems from inadequate input validation and memory handling during the processing of malformed PDF documents that are intended to be converted into HTML format. The flaw manifests when the application encounters specially crafted PDF files that trigger unexpected behavior in the conversion process, leading to application termination or system instability. Such vulnerabilities are particularly concerning in environments where PDF processing is automated or exposed to untrusted input sources, as they can be exploited to disrupt legitimate services without requiring elevated privileges or complex attack vectors.
The technical root cause of this vulnerability lies in the insufficient sanitization of PDF file structures during the HTML conversion process. When pdftohtml processes a maliciously crafted PDF, it fails to properly handle malformed or unexpected data structures within the document, resulting in memory corruption or stack overflow conditions that ultimately cause the application to crash. This type of vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and CWE-122, which covers stack-based buffer overflow scenarios. The flaw demonstrates characteristics of improper input validation where the application does not adequately check the integrity and structure of incoming PDF data before attempting conversion operations, making it susceptible to exploitation through carefully constructed malicious payloads.
The operational impact of CVE-2020-27778 extends beyond simple service disruption, as it can affect organizations relying on automated PDF processing workflows, web applications, or document management systems that utilize Poppler's pdftohtml functionality. Attackers can leverage this vulnerability to perform targeted denial of service attacks against systems processing PDF files, potentially causing cascading failures in document processing pipelines or web services that depend on reliable PDF conversion capabilities. The vulnerability's remote exploitation capability means that malicious actors can trigger the flaw without physical access to the target system, making it particularly dangerous in cloud environments or public-facing applications. This aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how vulnerabilities in document processing libraries can be weaponized to compromise availability of critical business services.
Mitigation strategies for CVE-2020-27778 should focus on immediate patching of affected Poppler versions, implementing input validation measures for PDF files before processing, and deploying application-level sandboxes or containerization techniques to isolate PDF conversion processes. Organizations should also consider implementing rate limiting and input sanitization controls for PDF processing endpoints, along with monitoring for unusual patterns in document conversion requests that might indicate exploitation attempts. The fix typically involves updating to Poppler versions that include proper input validation and memory handling improvements, while security teams should monitor for similar vulnerabilities in related PDF processing components and ensure comprehensive testing of document conversion workflows before deployment.