CVE-2026-24061: The Telnetd Bug That Turns "Secure" Networks Into Root Access

When "Everything Is Patched" Still Leads to Root

A lot of security programs look strong on paper.

• Perimeter hardened.
• Passwords rotated.
• Tools updated.
• Vulnerability scanners green.
• Security policies in place.

And yet, one overlooked service or one unexpected flaw in a trusted component can undo all of it in seconds.

That is exactly why CVE-2026-24061 matters.

This Telnet related vulnerability is a reminder that "secure" does not mean "safe from compromise." It means "harder to compromise." And threat actors love the easiest path.

What is CVE-2026-24061, briefly

CVE-2026-24061 is a critical authentication bypass in GNU InetUtils telnetd. It affects versions 1.9.3 through 2.7 and carries a CVSS 9.8 severity rating.

At a high level, the Telnet daemon passes an attacker controlled USER value into the system login process without properly sanitizing it, which can lead to argument injection and an authentication bypass that results in root access.

This issue was publicly disclosed via a security advisory by GNU contributor Simon Josefsson, and the vulnerability was originally found and responsibly reported by Kyu Neushwaistein (Carlos Cortes Alvarez).

Even more concerning, researchers observed real world activity quickly after disclosure, and there are reports of a large global Telnet exposure footprint.

Why this feels like a "backdoor" (even though it is not)

No one planted a deliberate backdoor here. It is a bug.

But from an attacker's point of view, the outcome looks similar: a path to root that bypasses the controls you rely on.

This is the uncomfortable lesson: Even fully legitimate, widely used, and recently updated software can contain a mistake that opens a door you did not know existed.

And we do not know how many similar weaknesses are exploited every day by criminal groups or state sponsored actors without ever being publicly disclosed.

The "secure client" scenario that still fails

Imagine a client with:

• A well structured segmented network.
• Strong perimeter controls and hardened internet facing services.
• Regular patching and modern endpoint protection.
• Secure password lifecycle and MFA.
• Up to date tools across servers and network appliances.

Now add one detail that is common in the real world:

A legacy management service still exists somewhere, maybe on an old appliance, an embedded Linux box, a lab segment, an OT network, or a "temporary" admin shortcut that never got removed. Telnet is a classic example because it keeps showing up in places people forget.

If an attacker gets any foothold, stolen credentials, a compromised VPN endpoint, a phished workstation, a supplier breach, the perimeter is no longer the main problem.

Inside the network, that forgotten Telnet service plus a vulnerability like CVE-2026-24061 can become the shortest route to privilege escalation and lateral movement.

Why assumed breach testing matters

Traditional penetration tests often focus on "can we get in."

Assumed breach flips the question to "what happens once someone is already in."

That difference matters because modern breaches rarely fail at the perimeter forever. Attackers try many options, including suppliers and identity attacks, until one works.

An assumed breach style test validates things your patching dashboard cannot:

• Can an attacker pivot between VLANs and segments.
• Can they reach management planes and admin services.
• Can they escalate to domain or root level privileges.
• Can they exfiltrate data without being detected.
• Can your SOC actually see the attacker path in time to respond.

CVE-2026-24061 is a perfect story for this approach because it shows how a single service can turn internal access into full control.

What companies should do now

Here are practical steps that reduce the risk from Telnet class issues and similar "unexpected root doors":

• Eliminate Telnet wherever possible: Replace it with SSH or modern management channels. If Telnet must exist, isolate it aggressively.
• Find what you forgot you had: Maintain an asset inventory that includes services and listening ports. Continuously verify that port 23 and other legacy admin ports are not reintroduced by rebuilds, vendor images, or emergency changes.
• Patch fast, but plan for "no patch yet" reality: CVE-2026-24061 has fixes available upstream and patched releases are referenced by multiple advisories, but many real environments cannot update instantly. Compensating controls must exist: disable the service, restrict by IP, firewall it, or block at network boundaries.
• Segment management access like it is production data: Put management interfaces behind jump hosts, enforce MFA, and limit who can even route to them. Treat "internal" as hostile by default.
• Detection engineering for legacy protocols: Alert on Telnet usage, unexpected root logins, and abnormal authentication flows. Your controls should assume that someone will eventually find a forgotten service.

How Haxoris can help

If you want to turn this lesson into measurable security improvements, Haxoris can support with:

• Assumed breach penetration testing.
• Internal network and Active Directory security testing.
• External attack surface and perimeter testing.
• Purple team exercises.
• Security hardening reviews.

Final thought

CVE-2026-24061 is not just a Telnet story.

It is a visibility story. A testing story. A humility story.

Because the uncomfortable truth in infrastructure security is this: You can do many things right and still lose to one overlooked detail.

If you assume breach and test like an attacker, you find those details before the attacker does.