CVE-2026-63276: Stack buffer overflow in CFF to Type 1 font conversion
LibreOffice converts CFF fonts to Type 1 when it subsets a font, which happens when a document is exported to PDF, and CFF fonts may be embedded in documents. A stack buffer overflow existed in that conversion. The converted operators were written into a fixed size buffer with no check that they still fit, so a glyph emitting many operators wrote past the end of the buffer. In fixed versions the remaining capacity is tracked and the conversion stops when it is used up.
Affected Software
Event History
Frequently Asked Questions
When can the vulnerable conversion path be reached?
It is reached when LibreOffice subsets a CFF font, which occurs when exporting a document to PDF. CFF fonts can be embedded in documents, so a document containing such a font can trigger the conversion during export.
What is required to trigger the overflow?
A CFF glyph must emit enough converted operators to exceed the fixed-size stack buffer used by the CFF-to-Type-1 conversion. The overflow occurs because the vulnerable conversion did not check whether additional operators still fit in that buffer.
How do fixed versions prevent this issue?
Fixed versions track the remaining buffer capacity during conversion and stop the conversion when that capacity is exhausted.