CVE-2026-98755 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
tty: vcc: zero-initialize control packet in vcc_send_ctl()
The stack-allocated struct vio_vcc pkt was partially initialized, leaving the tag.stype_env field uninitialized before being sent via ldc_write(), potentially leaking kernel stack data to the LDC peer.
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Analysis
by VulDB Data Team • 10/19/2026
This vulnerability represents a critical information disclosure flaw within the Linux kernel's virtual console and tty subsystem, specifically affecting the vcc_send_ctl function in drivers/tty/vcc.c. The root cause lies in improper memory initialization practices where a structure named vio_vcc is allocated on the stack but only partially initialized before being transmitted to an external entity via the ldc_write interface. In C programming, local variables that are not explicitly zeroed out retain whatever data previously existed at those memory addresses from prior function calls or system operations. This oversight results in the tag.stype_env field containing stale kernel stack data rather than a defined value.
The operational impact of this flaw is significant because it allows for the leakage of sensitive kernel memory contents to an LDC peer, which typically refers to a virtual machine monitor or another domain in virtualized environments using Logical Domain Control protocols. By sending uninitialized stack bytes over the network interface managed by the driver, an attacker with access to the receiving side can potentially reconstruct parts of the kernel's internal state. This includes potential exposure of pointers, cryptographic keys, passwords, or other confidential information that was recently processed by the kernel and left on the stack without being cleared after use. Such leaks undermine the confidentiality guarantees expected in secure computing environments and violate fundamental principles of memory isolation between domains.
From a vulnerability classification perspective, this issue aligns with CWE-200: Exposure of Sensitive Information to an Unauthorized Actor, as it involves the accidental disclosure of internal system data through improper handling of uninitialized variables. It also relates closely to CWE-908: Use of Uninitialized Resource, highlighting the failure to properly initialize a variable before its first use in a security-sensitive context. In terms of attack vectors and tactics, this vulnerability facilitates information gathering techniques described under MITRE ATT&CK technique T1074: Data Staged or Collected for Exfiltration, where an adversary might leverage such leaks to map out the target environment's memory layout or extract credentials stored in kernel space during previous operations.
Mitigation strategies primarily involve ensuring that all structures passed across trust boundaries are fully initialized before transmission. The specific fix implemented by developers involves zero-initializing the entire vio_vcc structure using standard functions like memset prior to populating its fields. This ensures that any unused bytes within the struct default to null values rather than retaining potentially sensitive residual data from previous stack frames. Additionally, static analysis tools and compiler warnings such as -Wuninitialized should be enabled during kernel development to catch similar issues early in the coding phase. For deployed systems, applying the latest security patches provided by Linux distribution maintainers is essential to resolve this flaw and prevent potential exploitation through network-based information leakage channels.