CVE-2026-53402 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
fbdev: fbcon: fix out-of-bounds read in err_out of fbcon_do_set_font()
When fbcon_do_set_font() fails (e.g., due to a memory allocation failure inside vc_resize() under heavy memory pressure), it jumps to the `err_out` label to roll back the console state. However, the current rollback logic forgets to restore the `hi_font` state, leading to a severe state machine corruption.
Earlier in the function, `set_vc_hi_font()` might be called to change `vc->vc_hi_font_mask` and mutate the screen buffer. If `vc_resize()` subsequently fails, the `err_out` path restores `vc_font.charcount` but entirely skips rolling back the `vc_hi_font_mask` and the screen buffer.
This mismatch leaves the terminal in a desynchronized state. Because `vc_hi_font_mask` remains set, the VT subsystem will still accept character indices greater than 255 from userspace and write them to the screen buffer. Subsequent rendering calls (e.g., `fbcon_putcs()`) will then use these inflated indices to access the reverted, 256-character font array, leading to a deterministic out-of-bounds read and potential kernel memory disclosure.
Fix this by adding the missing rollback logic for the `hi_font` mask and screen buffer in the error path.
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability described affects the linux kernel's framebuffer console subsystem particularly within the fbcon_do_set_font() function where an out-of-bounds read occurs due to improper state rollback during error conditions. This issue represents a critical security flaw that can lead to information disclosure and potential system instability when handling font changes in virtual terminal environments.
The technical root cause stems from incomplete error handling logic in the fbcon_do_set_font() function where memory allocation failures during vc_resize() operations trigger an err_out label jump for state rollback. However, this rollback process neglects to restore the hi_font state information which includes vc->vc_hi_font_mask and associated screen buffer modifications. The vulnerability manifests when set_vc_hi_font() is called earlier in the function to modify vc->vc_hi_font_mask and mutate the screen buffer, but subsequent failure in vc_resize() leaves these changes unreverted.
This creates a state machine corruption scenario where the virtual terminal subsystem maintains inconsistent internal state information. The vc_hi_font_mask remains set even though the font data structure has been reverted to its original 256-character array configuration, creating a mismatch between expected and actual buffer boundaries. When userspace applications submit character indices exceeding 255, the VT subsystem accepts these inputs due to the preserved hi_font_mask setting and writes them to the screen buffer.
Subsequent rendering operations such as fbcon_putcs() utilize these inflated indices to access the reverted font array which only contains 256 characters, resulting in deterministic out-of-bounds memory access. This predictable memory violation can lead to kernel memory disclosure since the out-of-bounds read may expose sensitive data from adjacent memory locations within kernel space. The vulnerability specifically impacts systems using framebuffer console drivers and virtual terminal functionality where dynamic font resizing operations occur under memory pressure conditions.
The fix requires implementing comprehensive rollback logic for hi_font mask and screen buffer state in the error path, ensuring that all modifications made during font change operations are properly reverted when failures occur. This addresses the mismatch between the preserved vc_hi_font_mask setting and the reverted 256-character font array structure, preventing the out-of-bounds access condition while maintaining system stability.
This vulnerability aligns with CWE-129 Input Validation and Output Handling, specifically addressing improper handling of buffer boundaries and state management in kernel space operations. The issue demonstrates characteristics consistent with ATT&CK technique T1068, where privilege escalation through kernel memory corruption can occur via improper state handling. The fix ensures proper state machine integrity by maintaining synchronization between font mask settings and actual font data structures during error recovery scenarios, preventing unauthorized memory access patterns that could be exploited for information disclosure attacks.