Naar aanleiding van de kwetsbaarheid die eind januari werd ontdekt, waardoor verbinding kon worden gemaakt als root-gebruiker zonder wachtwoordverificatie, zijn er in de telnetd-server van de GNU InetUtils verschillende methoden voor privilege-escalatie ontdekt, die het gevolg zijn van de onvolledige oplossing van de kwetsbaarheid in 1999 (CVE-1999-0073). <\/p>\n
De kwetsbaarheden zijn ontstaan door de mogelijkheid binnen telnetd om omgevingsvariabelen van de client naar de server te verzenden via de ENVIRON-optie. Dergelijke omgevingsvariabelen worden ingesteld en verwerkt in de context van het telnetd-proces en worden doorgegeven aan de door het proces opgestarte kindprocessen, waaronder het met root-rechten uitgeroepen proces \/bin\/login. De kwetsbaarheid CVE-1999-0073 stelde de telnet-client in staat om de omgevingsvariabele LD_LIBRARY_PATH door te geven, waarvan de instelling leidt tot het laden van de door de gebruiker opgegeven gedeelde bibliotheek bij het starten van het login-proces. Wanneer bestanden naar een systeem kunnen worden geladen dat telnet-verbindingen ondersteunt, kan een aanvaller een speciaal opgemaakte bibliotheek laden en deze met root-rechten laten laden. <\/p>\n
In telnetd from the GNU InetUtils package, a vulnerability was fixed by blocking dangerous environment variables through filtering for masks 'LD_', 'LIBPATH', 'ENV', 'IFS' and '_RLD_'. However, the environment variable 'CREDENTIALS_DIRECTORY', which is processed during the launch of \/usr\/bin\/login, was not blocked. With this environment variable, a user could change the directory with the credential settings and place a file login.noauth with the value 'yes', which activates login without a password (similar to passing the '-f' flag to the login process). This setting applies to all users, including root. <\/p>\n
The attack involves an unprivileged user creating a subdirectory in their home directory, uploading the login.noauth file into it, and trying to log in by setting the environment variable 'CREDENTIALS_DIRECTORY=created_directory' and passing the environment variable 'USER=root' (telnet has an automatic connection mode in which the username is taken not from the command line but passed through the USER environment variable). An example of an exploit. <\/p>\n
Daarna is er een andere manier ontdekt om root-toegang te verkrijgen via telnetd, gerelateerd aan de manipulatie van de omgevingsvariabelen OUTPUT_CHARSET en LANGUAGE, die worden verwerkt door de GNU gettext-bibliotheek, en de omgevingsvariabele GCONV_PATH, die wordt gebruikt in glibc. Door de omgevingsvariabelen OUTPUT_CHARSET en LANGUAGE in te stellen, kan een aanvaller de functionaliteit voor het converteren van tekenencoderingen in gettext activeren, wat de functie iconv_open() oproept. Bij de uitvoering van de functie iconv_open() bij het laden van het configuratiebestand gconv-modules, wordt het pad berekend rekening houdend met de omgevingsvariabele GCONV_PATH. Door het invoegen van het bestand gconv-modules kan laadbare aangepaste gedeelde bibliotheek tijdens het afgeven van een gelokaliseerde reeks door het login-proces worden georganiseerd. <\/p>\n
CVE identifiers have not yet been assigned to the noted vulnerabilities. As a protection method, the use of a whitelist of acceptable values ('TERM', 'DISPLAY', 'USER', 'LOGNAME', and 'POSIXLY_CORRECT') is being considered, blocking all other environment variables, similar to how environment variables are handled in OpenSSH. The vulnerabilities have been confirmed in the GNU InetUtils package, implementation. de server<\/a> telnetd die wordt geleverd in Debian, Ubuntu en afgeleide distributies. Er zijn momenteel geen correcties voor GNU InetUtils beschikbaar. Rocky Linux 9 biedt een gemodificeerd telnetd dat niet kwetsbaar is, waarin in plaats van filtering van gevaarlijke omgevingsvariabelen een whitelist-controle is opgenomen. De whitelist-filters zijn ook ge\u00efmplementeerd in telnetd van FreeBSD. In OpenBSD is telnetd in 2005 uit het systeem verwijderd. \u0421\u043b\u0435\u0434\u043e\u043c \u0437\u0430 \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u043d\u043e\u0439 \u0432 \u043a\u043e\u043d\u0446\u0435 \u044f\u043d\u0432\u0430\u0440\u044f \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c\u044e, \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u0432\u0448\u0435\u0439 \u043f\u043e\u0434\u043a\u043b\u044e\u0447\u0438\u0442\u044c\u0441\u044f \u043f\u043e\u0434 \u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u0435\u043b\u0435\u043c root \u0431\u0435\u0437 \u043f\u0440\u043e\u0432\u0435\u0440\u043a\u0438 \u043f\u0430\u0440\u043e\u043b\u044f, \u0432 \u0441\u0435\u0440\u0432\u0435\u0440\u0435 telnetd \u0438\u0437 \u043d\u0430\u0431\u043e\u0440\u0430 GNU InetUtils \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u043e \u043d\u0435\u0441\u043a\u043e\u043b\u044c\u043a\u043e \u0441\u043f\u043e\u0441\u043e\u0431\u043e\u0432 \u043f\u043e\u0432\u044b\u0448\u0435\u043d\u0438\u044f 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\u043e\u043f\u0446\u0438\u0438 ENVIRON. \u041f\u043e\u0434\u043e\u0431\u043d\u044b\u0435 \u043f\u0435\u0440\u0435\u043c\u0435\u043d\u043d\u044b\u0435 […]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":8,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-162791","post","type-post","status-publish","format-standard","hentry","category-news"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\n","aioseo_head_json":{"title":"\ud83e\udd47Een reeks nieuwe kwetsbaarheden in telnetd die root-privileges op het systeem kunnen verkrijgen | ProHoster","description":"Na de in januari ontdekte kwetsbaarheid, waarmee verbinding kon worden gemaakt als gebruiker root zonder wachtwoordverificatie, zijn er verschillende 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Bron: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"