CVE-2026-94029: Apache MINA SSHD: Memory exhaustion in SFTP v6 check-file-name/check-file-handle extension
Server-side memory exhaustion in Apache MINA SSHD 1.0.0 to 2.19.0 and 3.0.0-M1 to 3.0.0-M5, component sshd-sftp, in the SFTP v6 check-file-name/check-file-handle extension. Apache MINA SSHD is a Java library for client-side and server-side SSH.
Using a very small "block size" (for instance 256, which is the minimum) on a huge file generates many (file size / block size) hashes. The resulting SFTP reply message was accumulated fully in memory server-side, which could, with a suitably large (possibly sparse) file exhaust the server-side memory, taking down the server.
Users are recommended to upgrade to version 2.20.0 or 3.0.0-M6, which fix this issue by imposing a maximum limit on the size of the reply. Many SFTP implementations have a general limit on the size of SFTP messages anyway; typically 256kB as in OpenSSH or also in Apache MINA SSHD.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 2.20.0 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 3.0.0-M6
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Servers using the sshd-sftp component in Apache MINA SSHD versions 1.0.0 through 2.19.0 or 3.0.0-M1 through 3.0.0-M5 are affected when the SFTP v6 check-file-name or check-file-handle extension is available.
What does an attacker need to trigger the memory exhaustion?
The attacker needs SFTP access with the privileges required to invoke the affected extension against a huge, potentially sparse file. A very small block size, such as the minimum value of 256, causes the server to generate a large number of hashes and accumulate the full reply in memory.
How can this be remediated?
Upgrade Apache MINA SSHD to version 2.20.0 or 3.0.0-M6. These releases impose a maximum limit on the reply size.
Is there a mitigation if an upgrade cannot be applied immediately?
Using an SFTP implementation or configuration that enforces a general SFTP message-size limit can reduce exposure. The provided information notes that a 256 kB limit is typical in OpenSSH and Apache MINA SSHD.