CVE-2026-63274 in LibreOffice
Summary
by MITRE • 09/22/2026
LibreOffice Draw can import PDF documents. A heap buffer overflow existed when importing a stream object. The length of the stream was taken from the object's own dictionary and was not checked against the number of bytes actually present, so copying the stream read and wrote past the end of the buffer holding it. In fixed versions the declared length is clamped to the bytes actually read.
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Analysis
by VulDB Data Team • 09/22/2026
The vulnerability identified in LibreOffice Draw stems from a critical heap-based buffer overflow located within the PDF import module. This component is responsible for parsing Portable Document Format files, specifically handling stream objects which contain compressed or raw data segments essential for rendering graphics and text. The core technical flaw arises during the initialization of these streams, where the application retrieves the declared length of the data from the object's internal dictionary structure without performing adequate bounds checking against the actual number of bytes available in the input buffer. This lack of validation allows an attacker to craft a malicious PDF file containing a stream with a falsely inflated size declaration. When LibreOffice processes this malformed document, it allocates memory based on the declared length or attempts to copy data according to that length, leading to writes beyond the allocated heap boundaries.
This specific flaw is classified under CWE-120, which denotes Buffer Copy without Checking Size of Input, and more specifically as a Heap-based Buffer Overflow (CWE-122). The absence of rigorous input validation means that the application trusts untrusted data from the PDF file structure implicitly. By exploiting this condition, an attacker can achieve arbitrary code execution on the target system by overwriting adjacent heap metadata or function pointers with shellcode or controlled payloads. This aligns with MITRE ATT&CK technique T1203, which covers Exploitation for Client Execution, as the vulnerability is triggered when a user opens a specially crafted file using the vulnerable application. The impact extends beyond simple data corruption; it represents a severe security risk that can lead to full system compromise if exploited successfully in an unpatched environment.
The operational impact of this vulnerability is significant because LibreOffice Draw is widely used for creating and editing vector graphics, often involving complex PDF imports from various sources including the internet or email attachments. An attacker could distribute malicious PDFs via phishing campaigns or compromised websites to trigger the overflow when a victim opens the file in LibreOffice. The exploitability relies on the user's interaction with the application, but once triggered, the consequences are severe due to the potential for remote code execution. Mitigation strategies primarily involve applying vendor-provided patches that clamp the declared stream length to the actual number of bytes read from the input buffer. This ensures that memory operations remain within safe boundaries regardless of malicious size declarations in the file header. Users should maintain up-to-date versions of LibreOffice and exercise caution when opening PDF files from untrusted sources, utilizing sandboxed environments or document viewers with restricted permissions where possible to limit the blast radius of any potential exploitation attempts.