medium CVSS 4.2 EPSS 0.18%

CVE-2026-59997·OpenSSH vulnerability

internal-sftp in sshd in OpenSSH before 10.4 recognizes only the first 9 command-line arguments, which can be important if a later command-line argument would have helped to ensure the intended security properties of an SFTP connection.

Severity
medium
Software
OpenSSH
Fixed in
10.4
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at 0.18% — higher than 6% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Affected versions

Until: 10.4

Fixed in: 10.4

How to fix this CVE

Update OpenSSH to version 10.4p1-1 or later to resolve an argument parsing limitation in the internal-sftp subsystem. This vulnerability could allow attackers to bypass intended security configurations by exploiting how command-line arguments are processed during SFTP session initialization. Apply the security update immediately across all SSH-enabled servers.

sudo dnf update openssh-server openssh-clients

Defensia detects this vulnerability

How to check if you are affected

  1. Run 'ssh -V' or 'sshd -V' to check the installed OpenSSH version; affected versions are below 10.4p1-1
  2. Check if the SFTP subsystem is enabled in /etc/ssh/sshd_config by searching for 'Subsystem sftp' configuration entries
  3. Review SSH logs for SFTP session initialization attempts, typically found in /var/log/auth.log (Debian/Ubuntu) or /var/log/secure (RHEL/CentOS/Amazon Linux)
  4. After patching, restart the SSH daemon with 'sudo systemctl restart sshd' and verify the new version with 'sshd -V' to confirm the fix is active

FAQ

What is CVE-2026-59997?

CVE-2026-59997 is a vulnerability in OpenSSH's internal-sftp subsystem where only the first 9 command-line arguments are recognized during processing. This limitation can prevent later arguments that enforce important security restrictions from taking effect, potentially weakening SFTP connection security.

Is CVE-2026-59997 being actively exploited?

No, CVE-2026-59997 is not listed on the CISA Known Exploited Vulnerabilities (KEV) catalog and there are no publicly available exploits. However, it should still be patched promptly as a best practice for SSH security hardening.

What versions of OpenSSH are affected by CVE-2026-59997?

OpenSSH versions prior to 10.4p1-1 are affected. This includes all versions up to and including 10.3p1 and earlier.

How do I check if my server is vulnerable to CVE-2026-59997?

Run 'sshd -V' to display your installed version. If the output shows a version lower than 10.4p1-1, your server requires patching.

Does Defensia detect CVE-2026-59997?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If OpenSSH is installed on a monitored server, CVE-2026-59997 will appear in your dashboard with remediation steps.

Related OpenSSH CVEs

CVE-2008-0166CVSS 9OpenSSL 0.9.8c-1 up to versions before 0.9.8g-9 on Debian-based operating systems uses a random number generator that generates predictable numbers, which makes it easier for remote attackers to conduct brute force guessing attacks against cryptographic keys.
CVE-2016-6515CVSS 9The auth_password function in auth-passwd.c in sshd in OpenSSH before 7.3 does not limit password lengths for password authentication, which allows remote attackers to cause a denial of service (crypt CPU consumption) via a long string.
CVE-2016-10009CVSS 8.5Untrusted search path vulnerability in ssh-agent.c in ssh-agent in OpenSSH before 7.4 allows remote attackers to execute arbitrary local PKCS#11 modules by leveraging control over a forwarded agent-socket.
CVE-2016-6210CVSS 8.5sshd in OpenSSH before 7.3, when SHA256 or SHA512 are used for user password hashing, uses BLOWFISH hashing on a static password when the username does not exist, which allows remote attackers to enumerate users by leveraging the timing difference between responses when a large password is provided.
CVE-2018-15473CVSS 8.5OpenSSH through 7.7 is prone to a user enumeration vulnerability due to not delaying bailout for an invalid authenticating user until after the packet containing the request has been fully parsed, related to auth2-gss.c, auth2-hostbased.c, and auth2-pubkey.c.

References

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