CVE-2026-64089 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
batman-adv: tt: fix negative last_changeset_len
batadv_piv_tt::last_changeset_len len was declared as s16, but the field is never intended to hold a negative value. When a value greater than 32767 is assigned, it wraps to a negative signed integer.
In batadv_send_my_tt_response(), last_changeset_len is temporarily widened to s32. The incorrectly negative s16 value propagates into the s32, causing batadv_tt_prepare_tvlv_local_data() to allocate a full sized buffer but populates only a small portion of it with the collected changeset. All remaining bits are kept uninitialized.
Using an u16 avoids this type confusion and ensures that no (negative) sign extension is performed in batadv_send_my_tt_response().
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability described represents a critical integer overflow and type confusion issue within the batman-adv kernel module, specifically affecting the mesh routing protocol implementation. This flaw exists in the translation table handling mechanism where the last_changeset_len field is declared as a signed 16-bit integer s16, despite being logically intended to represent only non-negative values. The fundamental problem arises from the implicit assumption that this field will never exceed the positive range of a signed short integer, which becomes problematic when values surpass 32767, causing arithmetic wraparound to negative values due to two's complement representation.
The operational impact of this vulnerability manifests during the transmission of translation table responses within the batman-adv mesh network. When batadv_send_my_tt_response() processes the data, it temporarily widens the s16 value to s32 for processing purposes, but the corrupted negative value persists through this conversion process. This creates a scenario where batadv_tt_prepare_tvlv_local_data() allocates memory buffers based on the inflated (negative) value, resulting in excessive memory allocation while only populating a small fraction of the allocated space with actual data. The uninitialized memory segments remain untouched, creating potential information leakage and memory corruption vulnerabilities.
This type of vulnerability aligns with CWE-190, Integer Overflow or Wraparound, and CWE-129, Improper Validation of Array Index, as it demonstrates both the overflow condition and subsequent improper handling of the resulting invalid data. The issue also relates to ATT&CK technique T1059.001, Command and Scripting Interpreter, through potential exploitation vectors involving memory corruption that could lead to privilege escalation or denial of service conditions in networked environments. The root cause stems from inadequate type validation and improper handling of signed vs unsigned integer operations within kernel space networking code.
The proposed mitigation involves changing the data type from s16 to u16, which eliminates the possibility of negative values and prevents sign extension during type conversion processes. This solution addresses the fundamental type confusion by ensuring that the field can only represent valid non-negative values within the expected operational range while maintaining backward compatibility with existing protocols and data structures. The fix directly resolves the memory allocation inconsistency and prevents potential exploitation scenarios that could arise from uninitialized memory exposure in kernel networking modules.
The vulnerability demonstrates a classic example of how seemingly minor type declaration issues can lead to significant security implications in kernel space code, particularly in network protocol implementations where memory management and data integrity are paramount for system stability and security. This class of vulnerability is particularly concerning in mesh networking environments where multiple nodes may be affected simultaneously through propagated malicious data packets, making proper integer handling and validation essential for maintaining secure communication infrastructure.