GNU InetUtils telnetd is a legacy Telnet daemon exposing unencrypted port 23 and high-severity CVE-2026-24061 (CVSS 9.8) argument-injection (CWE-88) risks that may enable authentication bypass and root shell access, particularly across OT/IoT fleets; mitigate by replacing with SSH, isolating legacy enclaves, enforcing access controls, and prioritizing KEV-driven remediation.
GNU InetUtils telnetd still lurks in big networks, often unnoticed. People cite CVE-2026-24061 and the -f root exploit—scary, right? Let’s talk about how to spot it fast, rank the risk, and move to safer remote access without breaking uptime.
The Elephant in the Room: Why We Still Can’t Shake the Ghost of Telnet
The stubborn presence of GNU InetUtils telnetd in modern networks is not a mystery so much as a mix of habit, legacy dependencies, and tight maintenance windows. Many embedded platforms still ship with telnetd bundled in their firmware, where removing it risks voiding support or breaking fragile integrations. In plants, hospitals, and remote sites, teams inherit devices configured years ago, and change control often favors leaving port 23 untouched rather than risking downtime.
The security researcher Raphael Bastos posted a scathing critique of Linux security on his X account, centered on CVE-2026-24061, a critical vulnerability in the telnetd service of GNU inetutils. He highlights that this bug, which allows unauthenticated remote root access via a trivial command modification, existed undetected for nearly a decade and carries a near-maximum CVSS score of 9.8. The core of his argument is that Linux is built on “stacked hacks” and legacy code that lack proper oversight, in contrast to the “Security by Design” philosophy Bastos attributes to BSD systems and Apple’s XNU/Darwin kernel.
Linux sendo Linux. CVE crítico no telnetd do GNU inetutils dando root remoto sem autenticação (CVE-2026-24061) bug esse introduzido em 2015 e que ficou quase 10 anosativo no código. Nível? CVSS 9.8, exploração trivial, zero credencial, zero interação, basta mandar USER como “-f… pic.twitter.com/TNxz4MKou8
— coffnix (@coffnix) February 4, 2026
Furthermore, Bastos ridicules the Linux community for defending the system’s security, even as major vulnerabilities are normalized or patched only after years of exposure. He emphasizes that while telnet is largely obsolete in modern server environments, its continued default activation in high-end routers and switches makes this flaw particularly dangerous in the wild. Ultimately, he dismisses Linux as fundamentally insecure because of its architecture and reliance on poorly maintained, “patched-up” components, compared with the cleaner, more isolated designs of its Unix-like counterparts.
Risk that feels vintage but is painfully current
Telnet offers no encryption, which means credentials and sessions can be read or altered in transit, even on “trusted” segments. More troubling, recent issues tied to CVE-2026-24061 show that the danger is not only eavesdropping but also modern input-handling flaws such as Argument Injection (CWE-88), with a CVSS score of 9.8 underscoring impact. References to environment handling quirks, such as the USER variable and the so-called “-f root” style abuse, highlight a class of weaknesses that can lead to Root Shell Access in worst cases. When entries appear in the CISA Known Exploited Vulnerabilities catalog, the conversation shifts from theoretical to urgent.
Why organizations keep it anyway
Critical systems run on strict schedules, with upgrades planned months ahead and tested in lab twins before field rollout. Vendors sometimes ship only telnet-based diagnostics, and swapping gear can trigger recertification in regulated environments, stretching budgets and timelines. Operations teams also face thin staffing across far-flung sites, where “it still works” becomes a rational, if risky, default, especially when remote hands rely on simple tools that “always connect” to port 23.
Finding ghosts without breaking things
Discovery is harder than it looks because asset inventories lag behind reality, and IoT corners the perimeter with devices no one remembers buying. A careful sweep starts with reconciling configuration databases against passive flow data, mapping where port 23 appears, and confirming which hosts actually run GNU Network Utilities stacks. Safe, low-intensity checks during off-peak hours, combined with endpoint software inventories and firmware notes, help reduce the chance of tripping fragile hardware while still surfacing the telnet services that matter most.
A pragmatic path off telnet
Progress improves when the goal is to make remote access boring, not heroic. Segment telnet to isolated enclaves, put it behind bastion hosts, and prioritize cutover to SSH, serial console servers, or vendor-supported remote tooling with modern Remote Access Security. Where patches or replacements are not ready, tighten ACLs, add monitoring for suspicious port 23 activity, and set a sunset date that aligns with maintenance windows. In parallel, work with suppliers on supported firmware that removes telnetd by default, so the next refresh retires the ghost instead of inviting it back.
The Legacy Trap: Balancing Budget, Talent, and the “Safety First” Mandate
Legacy platforms rarely fail fast, which is why GNU InetUtils telnetd survives even when everyone agrees it should go. Teams face a three‑way pull: limited budgets, thin security talent, and a “safety first” mandate that treats uptime as a constraint rather than a goal. In practice, the calculus often favors leaving port 23 in place during tight maintenance windows, deferring change until the next outage or capital cycle.
The risk profile, however, does not wait. Findings linked to CVE-2026-24061 and Argument Injection (CWE-88) raise the stakes beyond simple eavesdropping, with a CVSS 9.8 score and a discussion of authentication-bypass paths that could lead to high‑impact compromise. When devices are added to the CISA Known Exploited Vulnerabilities catalog, the governance conversation shifts from “nice to fix” to “mandated remediation,” especially when IoT perimeter risk bleeds into production zones.
Budget and procurement realities
Financial constraints are not just about license fees. Replacing or hardening telnetd can trigger vendor recertification, on‑site labor, and downtime that ripple across revenue lines. Many organizations model the total cost of delay against the estimated breach probability for remote access security gaps on port 23, then sequence work to align with planned outages. Smarter contracting adds support clauses for the deprecation of GNU Network Utilities and for SBOM visibility, ensuring the next hardware refresh retires telnetd without unexpected costs.
Talent and operations
OT and network teams juggle scarce expertise, so even simple changes compete with incident queues and compliance tasks. Documentation ages quickly, runbooks drift, and a single missed step can interrupt a plant line. To counter this, leaders lean on repeatable builds, golden images, and low‑impact discovery to locate telnet services without disturbing fragile assets. Cross‑training ops and security, plus light automation for asset and firmware inventory, helps turn telnet removal from a hero project into a routine change.
Safety first without standing still
“Safety first” should not equal “no change.” Many programs reduce exposure by segmenting legacy enclaves, funneling access through hardened bastions, and enforcing tight allowlists while planning the final cutover to SSH. Measurable objectives—such as shrinking the count of port 23 endpoints each quarter or setting an SLO for KEV remediation—keep momentum without risking production stability. Over time, compensating controls, continuous monitoring, and vendor‑supported firmware updates make remote access predictable and, most importantly, boring.
The Modern Audit: Using AI Agents and Continuous Discovery to Kill Technical Debt
Modern audits work best when they are continuous and machine‑assisted. AI agents watch networks, endpoints, and repositories to surface hidden technical debt, such as GNU InetUtils telnetd running on port 23. Instead of one‑time scans, they correlate observations over days and weeks, revealing patterns that a busy team would miss and translating raw signals into clear, actionable context.
Discovery begins with a passive‑first posture to protect fragile OT and IoT assets. Agents learn typical traffic, banner hints, and firmware traits to spot legacy services without causing noise. When telnet exposure is detected, the system fingerprints hosts, links them to owners and maintenance windows, and builds a change path that aligns with the safety‑first mandate while maintaining momentum toward removal.
Intelligent enrichment and risk signals
Findings gain weight when they are enriched with software lineage and SBOM details. By linking telnet banners to the GNU Network Utilities packages, the audit can flag issues related to CVE-2026-24061, note the CVSS 9.8 severity, and cross-reference CISA Known Exploited Vulnerabilities. Signals about Argument Injection (CWE-88), possible Authentication Bypass paths, or misuse of the USER environment variable help convey impact without exposing methods, and frame why urgent attention outperforms deferral.
From code to change tickets
AI agents extend beyond the network into code and configuration. They scan infrastructure‑as‑code, init scripts, and service files for telnetd references, legacy inetd/xinetd directives, or unsafe flags like a “-f root” pattern in historical snippets. Rather than stopping at an alert, they propose diffs that replace telnet with SSH, outline test steps for lab twins, and assemble rollback plans that fit the site’s maintenance choreography.
Continuous discovery closes the loop by verifying outcomes. After a change, agents confirm that port 23 is gone, compensating controls remain in place, and telemetry shows no drift. Dashboards track the rate at which telnet endpoints decline, the age of unresolved exposures, and the time to remediate KEV‑listed items. Over time, these feedback cycles shrink technical debt, turn risky exceptions into standard work, and make remote access security predictable rather than heroic.
The Manager’s Choice: The Hard Road to a Long Career
A long career in infrastructure and security often depends on choosing visible, defensible actions over clever shortcuts. When GNU InetUtils telnetd is still present, the durable path is to acknowledge the exposure on port 23, map ownership, and commit to staged reduction rather than quiet acceptance. The choice is not dramatic; it is steady and documented, trading speed for traceability and aligning with the organization’s tolerance for change.
Risk framing matters because it sets the tone for funding and patience. References to CVE-2026-24061, the CVSS 9.8 score, and patterns such as Argument Injection (CWE-88), potential authentication bypass, or misuse of the USER environment variable communicate impact without triggering operational panic. When similar issues are listed in the CISA Known Exploited Vulnerabilities catalog, leaders can justify investment as mandatory hygiene, distancing themselves from any appearance of ignoring a known Remote Access Security gap.
Stakeholder alignment without heroics
Managers balance the realities of Legacy OT Security, thin engineering capacity, and a safety mandate that resists disruption. The prudent move is to secure consensus on change windows, document compensating controls, and sequence cutovers by business criticality. This framing treats telnet removal as a continuity task rather than a one‑off crusade, easing collaboration with operations teams who must keep lines running while debt is retired.
Metrics that protect both business and careers
Clear measures anchor difficult trade‑offs. Leaders track the number of telnet endpoints, the share placed behind bastions, and the mean time to remediate items associated with KEV listings. Trend lines for IoT perimeter risk and enclave segmentation show progress even when total eradication is months away. These metrics turn strategy reviews into evidence‑based updates, reinforcing that exposure is shrinking and that configuration drift is being managed.
Vendor and governance choices often decide whether progress sticks. Contracts should require SBOMs that explicitly identify GNU Network Utilities components, sunset clauses for telnetd, and supported migration paths to SSH. Change records tie each retirement to asset owners and maintenance slots, while tabletop exercises rehearse responses to attempted port 23 exploitation without revealing sensitive methods or Proof of Concept (PoC) details. Over time, this rhythm signals reliability to executives and auditors and builds a track record that keeps careers resilient.
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