# CVE-2026-59846: libssh shell metacharacter injection in ProxyCommand username expansion

Source: https://junglewise.ai/threats/cve-2026-59846-libssh-shell-metacharacter-injection-in-proxycommand-username  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-21. Updated: 2026-07-21  
License: CC BY 4.0 with a link back

CVE-2026-59846 · Severity: low · CVSS 3.9 · Published 2026-07-21

A security flaw exists in libssh, a library used by applications to provide secure communication services. When a program uses this library to connect to a server using a specific proxy configuration, a specially crafted username can trick the system into executing unintended shell commands. This could allow a local attacker to view sensitive environment variables or interfere with how the application operates.

Technologies: [Libssh](https://junglewise.ai/threats/technologies/libssh), [Red Hat Enterprise Linux 10](https://junglewise.ai/threats/technologies/enterprise-linux-10), [Red Hat Enterprise Linux 8](https://junglewise.ai/threats/technologies/enterprise-linux-8), [Red Hat Enterprise Linux 9](https://junglewise.ai/threats/technologies/enterprise-linux-9). Vendors: [Libssh](https://junglewise.ai/threats/vendors/libssh), [Red Hat](https://junglewise.ai/threats/vendors/red-hat).

## Quick answers

**Is CVE-2026-59846 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-59846 being exploited in the wild.

**How severe is CVE-2026-59846?** Low severity, with a CVSS score of 3.9, published 21 July 2026.

**Which products and versions are affected?** Red Hat Enterprise Linux 10 affected; Red Hat Enterprise Linux 8 affected; Red Hat Enterprise Linux 9 affected.

**Is there a fix for CVE-2026-59846?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-59846 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-59846?** Check whether you run Libssh, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8 or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A vulnerability exists in the ssh_check_username_syntax() function within src/misc.c of libssh. The validation path uses an incomplete filter for dangerous characters when expanding usernames through the %r token in ProxyCommand configurations. An attacker providing a specially crafted username containing shell metacharacters can influence shell expansion during ProxyCommand execution. This requires the client to combine untrusted username input with a ProxyCommand-style shell execution, leading to information disclosure of environment variables or unintended shell behavior.

## Affected products

- Red Hat Red Hat Enterprise Linux 8 affected
- Red Hat Red Hat Enterprise Linux 9 affected
- Red Hat Red Hat Enterprise Linux 10 affected
- Red Hat Red Hat Hardened Images affected
- libssh libssh

## Timeline

- 2026-07-08: disclosed: Reported via Red Hat Bugzilla
- 2026-07-21: advisory: NVD publication date

## References

- [https://access.redhat.com/downloads/content/package-browser/](https://access.redhat.com/downloads/content/package-browser/)
- [https://access.redhat.com/security/cve/CVE-2026-59846](https://access.redhat.com/security/cve/CVE-2026-59846)
- [https://bugzilla.redhat.com/show_bug.cgi?id=2498179](https://bugzilla.redhat.com/show_bug.cgi?id=2498179)

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