CVE-2026-24061: Bypass de Autenticación Remota en Telnetd de GNU InetUtils

Ruslan Mikhalov Jefe de Investigación de Amenazas en SOC Prime

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CVE-2026-24061: Bypass de Autenticación Remota en Telnetd de GNU InetUtils

Detection stack

AIDR
Alert
ETL
Query

Informe de Amenazas
Flujo de Ataque
Detecciones
Simulaciones

Resumen

CVE-2026-24061 es una vulnerabilidad de omisión de autenticación remota en GNU InetUtils telnetd que afecta a las versiones 1.9.3 hasta la 2.7. Un atacante no autenticado puede proporcionar una variable de entorno USER especialmente diseñada y pasarla a través de un cliente telnet utilizando las opciones -a o –login, habilitando un inicio de sesión que resulta en acceso a nivel root. El problema está calificado como CVSS 9.8. El alcance está limitado a GNU InetUtils telnetd (hasta 2.7); otras implementaciones de telnetd (incluyendo Cisco IOS, Microsoft, Netkit y BusyBox) no están afectadas. La explotación exitosa permite el acceso remoto y también se puede usar para lograr elevación de privilegios local a root. La mitigación más segura es identificar y deshabilitar Telnet por completo; las restricciones de red pueden reducir la exposición, pero solo eliminando el servicio se elimina el riesgo de elevación local a root.

Investigación

NSFOCUS CERT determinó que telnetd no valida correctamente la variable de entorno USER suministrada por el cliente. Al abusar de esta debilidad en la validación, un atacante puede omitir la lógica estándar de autenticación y obtener acceso root en hosts vulnerables Linux/Unix que ejecutan el daemon afectado.

Mitigación

Hay una solución disponible del proveedor para GNU InetUtils; los sistemas afectados deben actualizarse a una versión con parches. Si no se puede completar inmediatamente la aplicación de parches, deshabilite telnetd y migre a SSH. El endurecimiento interino adicional incluye la configuración de telnetd para usar un envoltorio de inicio de sesión personalizado y deshabilitar o prevenir el uso del parámetro -f cuando sea aplicable.

Respuesta

Identifique los sistemas que ejecutan telnetd y monitorice las sesiones de telnet invocadas con -a o –login, especialmente cuando se observen intentos remotos de establecer la variable de entorno USER. Priorice el despliegue de parches, deshabilite telnetd donde sea posible y refuerce los protocolos de administración remota cifrados para prevenir una re-explotación.

Flujo de Ataque

Aún estamos actualizando esta parte. Regístrate para recibir notificaciones

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Detecciones

Uso de Telnet [Posible Actividad LPE] (vía cmdline)

Equipo de SOC Prime

29 Ene 2026

Ver

Uso de Puertos Internos / Externos de Telnet (vía auditd)

Equipo de SOC Prime

29 Ene 2026

Ver

Uso de Puertos Internos / Externos de Telnet (vía zeek)

Equipo de SOC Prime

29 Ene 2026

Ver

Uso de Puertos Internos / Externos de Telnet (vía firewall)

Equipo de SOC Prime

29 Ene 2026

Ver

Simulación

Aún estamos actualizando esta parte. Regístrate para recibir notificaciones

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Name	Descripiton
PHPSESSID	Preserves user session state across page requests. Cookie generated by applications based on the PHP language. This is a general purpose identifier used to maintain user session variables. It is normally a random generated number, how it is used can be specific to the site, but a good example is maintaining a logged-in status for a user between pages.
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sp_r	Used to store information about authenticated User.
sp_a	Used to store information about authenticated User.

Name	Descripiton
tuuid	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded.
tuuid_last_update	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded.
um	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded.
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na_sc_x	Used by the social sharing platform AddThis to keep a record of parts of the site that has been visited in order to recommend other parts of the site.
APID	Collects anonymous data related to the user's visits to the website.
IDSYNC	Collects anonymous data related to the user's visits to the website.
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_cc_cc	Collects anonymous statistical data related to the user's website visits, such as the number of visits, average time spent on the website and what pages have been loaded. The purpose is to segment the website's users according to factors such as demographics and geographical location, in order to enable media and marketing agencies to structure and understand their target groups to enable customised online advertising.
_cc_dc	Collects anonymous statistical data related to the user's website visits, such as the number of visits, average time spent on the website and what pages have been loaded. The purpose is to segment the website's users according to factors such as demographics and geographical location, in order to enable media and marketing agencies to structure and understand their target groups to enable customised online advertising.
_cc_id	Collects anonymous statistical data related to the user's website visits, such as the number of visits, average time spent on the website and what pages have been loaded. The purpose is to segment the website's users according to factors such as demographics and geographical location, in order to enable media and marketing agencies to structure and understand their target groups to enable customised online advertising.
dpm	Via a unique ID that is used for semantic content analysis, the user's navigation on the website is registered and linked to offline data from surveys and similar registrations to display targeted ads.
acs	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded, with the purpose of displaying targeted ads.
clid	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded, with the purpose of displaying targeted ads.
KRTBCOOKIE_#	Registers a unique ID that identifies the user's device during return visits across websites that use the same ad network. The ID is used to allow targeted ads.
PUBMDCID	Registers a unique ID that identifies the user's device during return visits across websites that use the same ad network. The ID is used to allow targeted ads.
PugT	Registers a unique ID that identifies the user's device during return visits across websites that use the same ad network. The ID is used to allow targeted ads.
ssi	Registers a unique ID that identifies a returning user's device. The ID is used for targeted ads.
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wam-sync	Used by the advertising platform Weborama to determine the visitor's interests based on pages visits, content clicked and other actions on the website.
wui	Used by the advertising platform Weborama to determine the visitor's interests based on pages visits, content clicked and other actions on the website.
AFFICHE_W	Used by the advertising platform Weborama to determine the visitor's interests based on pages visits, content clicked and other actions on the website.
B	Collects anonymous data related to the user's website visits, such as the number of visits, average time spent on the website and what pages have been loaded. The registered data is used to categorise the users' interest and demographical profiles with the purpose of customising the website content depending on the visitor.
1P_JAR	These cookies are used to gather website statistics, and track conversion rates.
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NID	Google set a number of cookies on any page that includes a Google reCAPTCHA. While we have no control over the cookies set by Google, they appear to include a mixture of pieces of information to measure the number and behaviour of Google reCAPTCHA users.
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SIDCC	Security cookie to protect users data from unauthorised access.
SSID	Google set a number of cookies on any page that includes a Google reCAPTCHA. While we have no control over the cookies set by Google, they appear to include a mixture of pieces of information to measure the number and behaviour of Google reCAPTCHA users.
__utmx	This cookie is associated with Google Website Optimizer, a tool designed to help site owners improve their wbesites. It is used to distinguish between two varaitions a webpage that might be shown to a visitor as part of an A/B split test. This helps site owners to detemine which version of a page performs better, and therefore helps to improve the website.
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Name	Descripiton
_hjid	Hotjar cookie. This cookie is set when the customer first lands on a page with the Hotjar script. It is used to persist the random user ID, unique to that site on the browser. This ensures that behavior in subsequent visits to the same site will be attributed to the same user ID.
_hjIncludedInSample	This cookie is associated with web analytics functionality and services from Hot Jar, a Malta based company. It uniquely identifies a visitor during a single browser session and indicates they are included in an audience sample.
intercom-id-[xxx]	This cookie is used by Intercom as a session so that users can continue a chat as they move through the site.
intercom-session-[xxx]	Used to keeping track of sessions and remember logins and conversations.
demdex	Via a unique ID that is used for semantic content analysis, the user's navigation on the website is registered and linked to offline data from surveys and similar registrations to display targeted ads.
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IDE	Used by Google DoubleClick to register and report the website user's actions after viewing or clicking one of the advertiser's ads with the purpose of measuring the efficacy of an ad and to present targeted ads to the user.
r/collect	Used by Google DoubleClick to register and report the website user's actions after viewing or clicking one of the advertiser's ads with the purpose of measuring the efficacy of an ad and to present targeted ads to the user.
test_cookie	Used to check if the user's browser supports cookies.
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khaos	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.
put_#	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.
rpb	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.
rpx	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.
tap.php	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.