UBUNTU-CVE-2026-84267: Medium severity ubuntu/gvfs vulnerability
A flaw was found in the SFTP backend in gvfs. When mounting a share, a malicious SFTP server can cause readstring() to allocate a buffer with a certain length but the function does not verify that the buffer is completely filled, leaving the remainder of the buffer containing uninitialized heap contents. If the server sends a short FXPHANDLE reply, these uninitialized bytes are taken as the file handle. The client will then echo these uninitialized bytes back to the server on all subsequent requests using that handle. With a length of 128 bytes, this issue allows the malicious server to deterministically read uninitialized heap memory from the gvfsd-sftp process, leaking its heap base and the load address of the libgio library, resulting in a deterministic defeat of Address Space Layout Randomization (ASLR).
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
ubuntu/gvfsto a version that resolves this vulnerability.Fixed in 1.48.2-0ubuntu1.3 - Upgrade
Upgrade
ubuntu/gvfsto a version that resolves this vulnerability.Fixed in 1.54.4-0ubuntu1~24.04.5 - Upgrade
Upgrade
ubuntu/gvfsto a version that resolves this vulnerability.Fixed in 1.60.0-1ubuntu0.2
Event History
Frequently Asked Questions
Who is exposed to this issue?
Users or systems that mount an SFTP share through the gvfs SFTP backend are exposed when the SFTP server is malicious. The vulnerable component is the gvfsd-sftp process on Ubuntu systems using gvfs.
What does an attacker need to exploit it?
An attacker needs to operate or control an SFTP server that the victim mounts. No authentication or privileges on the client are required, but the victim must interact with the server by mounting its share.
What can the malicious server obtain?
A malicious server can cause gvfsd-sftp to send uninitialized heap bytes back in subsequent requests. Using a 128-byte handle, it can deterministically leak the process heap base and the load address of libgio, defeating ASLR for that process.