Backdoor Blues: Critical Linux Flaws Open the Gates for Attackers

The calm of IT departments worldwide was shattered this week as federal cybersecurity officials issued a stark warning: two major Linux vulnerabilities are being actively exploited, with attackers moving faster than ever to breach systems. For many, the discovery is a wake-up call about the risks lurking in overlooked or legacy services powering critical infrastructure.

Fast Facts

• Two Linux vulnerabilities - one in GNU Inetutils telnetd, one in the Linux kernel - have been added to CISA’s Known Exploited Vulnerabilities (KEV) catalog.
• CVE-2026-24061 allows remote attackers to bypass authentication and gain root access via the telnetd service.
• Over 200,000 internet-exposed systems may be running vulnerable Telnet services, with exploitation attempts already detected in the wild.
• CVE-2018-14634 enables local privilege escalation on systems with large memory but has not yet been seen exploited publicly.
• Federal agencies are under orders to patch these flaws by February 16, 2026.

The Anatomy of a Breach: How Attackers Are Breaking In

At the center of the storm is CVE-2026-24061, a critical flaw in the GNU Inetutils telnetd service, scoring a near-maximum 9.8 on the CVSS severity scale. This bug, introduced as far back as 2015 and only patched last December, allows anyone with network access to the login prompt to bypass authentication entirely. By manipulating the 'USER' environment variable, an attacker can trick the system into handing over a root shell - effectively full control - without ever providing a password.

Security researchers observed exploitation attempts within days of the flaw’s public disclosure. According to GreyNoise, at least 18 unique attack sources have been spotted scanning and attempting to compromise vulnerable servers, using the opening for reconnaissance, malware deployment, and persistent SSH access. The internet is awash with exposed Telnet services, but the real danger lies with those specifically running the GNU telnetd variant - estimated at hundreds of thousands, if not over a million, systems worldwide.

The second Linux flaw, CVE-2018-14634, is less dramatic in its exploitation but no less dangerous. It’s an integer overflow in the Linux kernel that allows a user with access to a privileged binary to escalate their privileges to root. The caveat? The attack requires systems with at least 32GB of RAM, a specification increasingly common in enterprise and cloud environments. While no in-the-wild exploitation has been reported yet, its addition to the KEV catalog signals that threat actors are likely taking notice.

These Linux bugs join a growing list of actively exploited vulnerabilities across platforms, including recent attacks on SmarterMail, Microsoft Office, and major network appliances. For defenders, the message is clear: patch early, patch often, and never underestimate the creativity - or speed - of attackers targeting even the oldest corners of your infrastructure.

Reflections: The Cost of Complacency

The rapid exploitation of these Linux flaws underscores a hard truth: legacy protocols and overlooked systems remain low-hanging fruit for cybercriminals. As attackers automate reconnaissance and exploitation, organizations must move just as swiftly to close gaps. The cost of delay is no longer measured in theoretical risk, but in breached systems, lost data, and disrupted operations.

WIKICROOK

• Authentication Bypass: Authentication bypass is a vulnerability that lets attackers skip or trick the login process, gaining access to systems without valid credentials.
• Root Shell: A root shell gives users full administrative control on Unix or Linux systems, allowing unrestricted command execution and system modifications. Use with caution.
• Remote Code Execution (RCE): Remote Code Execution (RCE) is when an attacker runs their own code on a victim’s system, often leading to full control or compromise of that system.
• Privilege Escalation: Privilege escalation occurs when an attacker gains higher-level access, moving from a regular user account to administrator privileges on a system or network.
• CVSS Score: A CVSS Score rates the severity of security vulnerabilities from 0 to 10, with higher numbers indicating greater risk and urgency for response.