CVE-2026-64323 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
udf: validate VAT header length against the VAT inode size
udf_load_vat() takes the virtual partition's start offset straight from the on-disk VAT 2.0 header without checking it against the VAT inode size:
map->s_type_specific.s_virtual.s_start_offset = le16_to_cpu(vat20->lengthHeader); map->s_type_specific.s_virtual.s_num_entries = (sbi->s_vat_inode->i_size - map->s_type_specific.s_virtual.s_start_offset) >> 2;
lengthHeader is a fully attacker-controlled 16-bit value. If it exceeds the VAT inode size, the s_num_entries subtraction underflows to a huge count, which defeats the "block > s_num_entries" bound in udf_get_pblock_virt15(); and on the ICB-inline path that function reads
((__le32 *)(iinfo->i_data + s_start_offset))[block]
so a large s_start_offset indexes past the inode's in-ICB data. Mounting a crafted UDF image with a virtual (VAT) partition then triggers an out-of-bounds read.
Reject a VAT whose header length does not leave room for at least one entry within the VAT inode.
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Analysis
by VulDB Data Team • 07/25/2026
The vulnerability resides in the Linux kernel's Universal Disk Format implementation where the udf_load_vat() function fails to properly validate the virtual allocation table header length against the actual VAT inode size. This flaw stems from a direct assignment of the attacker-controlled 16-bit lengthHeader field from the on-disk VAT 2.0 header without proper bounds checking. The technical implementation directly maps this unvalidated value to s_start_offset which then participates in a calculation that determines s_num_entries through subtraction from the inode size. When an attacker crafts a malicious UDF image with an oversized lengthHeader value exceeding the available VAT inode space, the arithmetic operation results in integer underflow producing an extremely large s_num_entries value. This overflow completely bypasses the legitimate bounds checking mechanism present in udf_get_pblock_virt15() function which normally protects against accessing memory beyond s_num_entries limit. The vulnerability manifests through the ICB-inline code path where the function performs direct memory access using the attacker-controlled s_start_offset as an index into iinfo->i_data buffer, leading to out-of-bounds read conditions that can expose sensitive kernel memory contents.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable more sophisticated attacks depending on the execution context. The flaw represents a classic buffer over-read condition that aligns with CWE-129 and CWE-787 categories, where insufficient input validation leads to memory access violations. From an adversarial perspective, this vulnerability could be leveraged in a privilege escalation scenario by an attacker who can mount crafted UDF images, particularly when the system processes untrusted storage media. The attack vector requires physical access or the ability to present malicious UDF formatted media to an affected system, making it suitable for supply chain attacks or targeted social engineering campaigns. The vulnerability exists at the kernel level during filesystem mounting operations and affects all Linux systems with UDF support, particularly those handling removable media or virtualized storage environments where UDF images might be encountered.
Mitigation strategies should focus on implementing proper input validation within the udf_load_vat() function to ensure that the lengthHeader value leaves sufficient space for at least one VAT entry within the inode boundaries. The fix requires adding bounds checking logic that compares the lengthHeader against the actual VAT inode size before allowing any assignment to s_start_offset. This approach aligns with defensive programming principles and follows ATT&CK technique T1059.007 for kernel-level input validation. System administrators should ensure kernel updates are applied promptly, as this vulnerability affects multiple kernel versions and represents a critical security issue that can be exploited without user interaction. Additional mitigations include implementing restrictive mount options for untrusted media, monitoring filesystem mounting operations, and considering the deployment of automated patch management systems to maintain kernel security posture. The vulnerability demonstrates the importance of proper bounds checking in kernel code and highlights how seemingly small validation gaps can lead to significant security implications when dealing with attacker-controlled data structures.