CVE-2026-63273 in LibreOffice
Summary
by MITRE • 09/22/2026
LibreOffice Draw can import PDF documents. A heap buffer overflow existed when importing an encrypted document. The length of the decryption key was taken from the document's own encryption dictionary and was used to fill a fixed size key buffer without being checked against it, so a length larger than that buffer wrote past its end. In fixed versions a declared key length larger than the buffer is rejected.
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Analysis
by VulDB Data Team • 09/22/2026
The vulnerability identified in LibreOffice Draw stems from an improper handling of encrypted PDF documents during the import process. As a specialized vector graphics editor within the LibreOffice suite, LibreOffice Draw supports importing Portable Document Format files to allow users to edit or manipulate their contents. However, when processing these imported documents, particularly those that are password-protected and encrypted, the application fails to adequately validate input parameters before performing memory operations. This specific flaw is classified as a heap buffer overflow, which corresponds to CWE-120 in the Common Weakness Enumeration standard. The root cause lies in how the decryption key length is extracted from the PDF's internal encryption dictionary. Instead of verifying that this declared length fits within the pre-allocated fixed-size buffer intended for storing the key data, the application blindly uses the value provided by the document itself to determine copy operations.
From a technical perspective, the operational mechanism of this flaw involves reading an integer value representing the key size directly from the untrusted PDF file structure. This value is then used as the count parameter in a memory copy function targeting a fixed-size buffer on the heap. Because there are no bounds checks performed prior to this operation, if the declared length exceeds the actual capacity of the destination buffer, data will be written beyond its allocated boundaries. In C and C++ based applications like LibreOffice, such out-of-bounds writes can corrupt adjacent memory structures, overwrite control data, or lead to arbitrary code execution depending on how the heap is laid out in memory at runtime. This type of vulnerability aligns with MITRE ATT&CK technique T1203, which covers exploitation for binary execution, as an attacker could potentially craft a malicious PDF that triggers this overflow to execute arbitrary commands within the context of the user running LibreOffice Draw.
The impact of this vulnerability is significant because it allows remote code execution through social engineering or automated distribution vectors where users are tricked into opening specially crafted PDF files. Since LibreOffice is widely used in enterprise and educational environments, successful exploitation could lead to a complete compromise of the victim's system privileges. The attacker gains the ability to run arbitrary code with the same permissions as the user, potentially leading to data theft, installation of malware, or further lateral movement within a network if the compromised machine serves as an entry point. This risk is heightened by the fact that PDFs are commonly exchanged via email and web downloads, making them a frequent target for phishing campaigns and drive-by attacks.
Mitigation strategies primarily involve updating LibreOffice to versions where this flaw has been patched. In fixed releases, developers implemented strict validation logic that checks whether the declared key length from the encryption dictionary exceeds the maximum allowed size of the internal buffer. If the value is found to be too large, the import operation is rejected safely without attempting the unsafe memory copy. Beyond software updates, users should exercise caution when opening PDF files obtained from untrusted sources and consider using sandboxed environments or virtual machines for viewing potentially malicious documents. Additionally, enabling automatic update mechanisms ensures that security patches are applied promptly as they become available, reducing the window of exposure to such vulnerabilities.