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CVE-2026-59679 is an out-of-bounds heap read/write vulnerability in the libXfont2 font-server client function fs_read_glyphs() in src/fc/fserve.c. The client allocates the per-character encoding[] array according to num_extents from an FS_QueryXExtents16 reply, but subsequently indexes that array using num_chars from a separate FS_QueryXBitmaps16 reply without validating that the latter count fits the allocation. A malicious or compromised font server can provide a small num_extents value followed by a large num_chars value, causing attacker-controlled accesses beyond the encoding[] heap allocation.
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A vulnerability tracked as CVE-2026-59679 affecting libXfont2 packages on Oracle Linux 7. The advisory indicates a network-accessible issue with high confidentiality, integrity, and availability impact, but high attack complexity.
An out-of-bounds heap read and write vulnerability in libXfont2's font-server client function fs_read_glyphs(). A malicious or compromised font server can provide inconsistent FS_QueryXExtents16 and FS_QueryXBitmaps16 response counts, causing accesses beyond the encoding[] array allocation.
A critical, remotely exploitable heap out-of-bounds read/write vulnerability in libXfont2's fs_read_glyphs() function. Inconsistent, unchecked font-server reply fields can let a malicious or compromised font server trigger memory corruption.
An out-of-bounds read/write vulnerability in the X.Org X11 libXfont2 Font Server Client encoding[] handling. It affects the libXfont2 package on Red Hat Enterprise Linux 8 systems covered by RHSA-2026:61995.
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