Summary Points
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Critical Vulnerability in Telnet: A decade-old authentication bypass flaw (CVE-2026-24061) in the GNU InetUtils telnetd server has been added to the CISA’s Known Exploited Vulnerability catalog, posing a risk of complete device control for attackers.
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Exposed Telnet Servers: Approximately 800,000 telnet instances are publicly exposed worldwide, often found on legacy IoT devices, presenting an alarming attack surface due to the protocol’s insecure nature.
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Urgent Responses Needed: Security experts urge immediate patching of vulnerable systems. The flaw’s simplicity makes it easy for attackers, emphasizing the necessity to limit public access to telnet ports.
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Rise in Telnet Usage: Despite being outdated and lacking security, telnet usage is increasing across various sectors, including government, with 4% of devices monitored still operating without secure alternatives like SSH.
Critical Vulnerability Discovered in Telnet Servers
Threat actors exploit a critical vulnerability in telnet servers, affecting hundreds of thousands of devices. This flaw, tracked as CVE-2026-24061, relates to an authentication bypass in the GNU InetUtils telnetd server. Recently, the US Cybersecurity and Infrastructure Security Agency (CISA) added this issue to its Known Exploited Vulnerability catalog. The vulnerability has existed for over a decade and could allow attackers complete control of affected devices.
The vulnerability originated in May 2015, increasing urgency as attackers have already begun to exploit it. Security experts highlight that the flaw enables remote authentication bypass through a simple argument injection. With around 800,000 exposed telnet instances worldwide, the risks are significant. Experts urge immediate action to mitigate these threats, as outdated systems often remain vulnerable.
Telnet’s Role in Today’s Threat Landscape
Despite being an outdated protocol, telnet persists in legacy systems and Internet of Things (IoT) devices. Many organizations expose telnet publicly, especially on older IoT equipment. Statistics reveal a concerning trend: platforms using telnet increased last year, particularly in government networks. This trend coincides with a decline in the use of the more secure Secure Shell (SSH) protocol.
Security professionals emphasize the need for organizations to remain vigilant. They recommend entirely avoiding telnetd servers. If using telnet is unavoidable, experts advise restricting network access to trusted clients and segmenting high-risk devices. Organizations must ensure they do not expose vulnerable telnet servers, particularly in critical infrastructure sectors.
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