CVE-2026-84268 in Red Hat
Summary
by MITRE • 09/01/2026
A flaw was found in the SFTP backend in gvfs. When mounting a share and reading a file, a malicious SFTP server can cause read_reply() to process a length that exceeds the size requested by the client. The function does not verify the server-provided length against the allocated buffer size, causing the operation to write past the intended boundaries. This issue allows a malicious server to corrupt adjacent heap memory in the gvfsd-sftp process, resulting in a denial of service as the process aborts upon detecting the heap corruption or potentially allowing arbitrary code execution.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 09/01/2026
The vulnerability identified within the SFTP backend implementation of GVFS represents a critical buffer overflow flaw that stems from insufficient validation of server-provided data lengths during file read operations. When a client mounts an SFTP share and initiates a request to retrieve specific content, the gvfsd-sftp daemon processes incoming packets from the remote server. The core technical defect lies in the read_reply function, which fails to perform essential boundary checks before processing the payload length advertised by the malicious SFTP server. Instead of verifying that the reported data size does not exceed the pre-allocated buffer capacity or the originally requested byte count, the application blindly trusts the server's assertion regarding the amount of data being transmitted. This lack of input validation allows an attacker to craft a specially crafted response packet containing a length field significantly larger than the actual available memory space allocated for that operation.
As a direct consequence of this logic error, the gvfsd-sftp process attempts to write the excess data into adjacent regions of heap memory beyond the intended buffer boundaries. This out-of-bounds write corrupts critical metadata structures and other objects residing in contiguous memory locations within the daemon's address space. The immediate operational impact is typically a denial of service condition, as modern operating systems employ various protections such as heap canaries or guard pages that detect this corruption almost instantaneously. Upon detection, the gvfsd-sftp process terminates abruptly to prevent further damage, effectively disrupting access to any SFTP shares mounted by the user and potentially causing instability in dependent applications that rely on GVFS for file system operations.
However, the severity of this vulnerability extends beyond simple service disruption because heap corruption provides a potent attack vector for arbitrary code execution under certain conditions. If an attacker can precisely control the data written past the buffer boundary, they may overwrite function pointers, virtual table entries, or other critical control flow structures within the process memory layout. By carefully crafting the overflow payload to include shellcode or return-oriented programming gadgets, it is possible to hijack the execution flow of the gvfsd-sftp daemon. Since this process often runs with the privileges of the authenticated user and may have access to sensitive files on the local system, successful exploitation could lead to full compromise of the client machine's security posture.
This vulnerability aligns closely with Common Weakness Enumeration CWE-120, which describes buffer copy without checking size limits, as well as CWE-787, indicating out-of-bounds write operations that allow writing data outside the intended boundary of a memory region. From an offensive perspective, this flaw facilitates exploitation techniques categorized under MITRE ATT&CK tactics such as Initial Access and Execution, specifically leveraging client-side software vulnerabilities to gain unauthorized control over target systems. The attack vector is classified as remote because it requires interaction with a malicious SFTP server rather than local access or physical proximity.
Mitigation strategies for this vulnerability primarily involve updating the gvfs package to versions where the read_reply function has been patched to strictly validate that the incoming data length does not exceed both the allocated buffer size and the client's original request parameters. System administrators should ensure that all endpoints are running updated software releases provided by their respective distribution vendors until official patches are available. In environments where immediate patching is not feasible, network-level controls such as firewalls or intrusion prevention systems can be configured to inspect SFTP traffic for anomalous packet sizes or malformed responses, although this may introduce latency and does not guarantee complete protection against sophisticated attacks. Users should also exercise caution when connecting to untrusted or unknown SFTP servers until the underlying software vulnerability is resolved.