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Shared Library Shimming for Password Harvesting

Shared Library Shimming for Password Harvesting. Rodney Thayer rodney@shmoo.com. Introduction. ‘Slimjim’ – a shared library shim PAM – Pluggable Authentication Modules Shared Library shimming The vulnerability The Slimjim code Demonstration Conclusions. Disclaimer.

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Shared Library Shimming for Password Harvesting

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  1. Shared Library Shimming for Password Harvesting Rodney Thayer rodney@shmoo.com

  2. Introduction • ‘Slimjim’ – a shared library shim • PAM – Pluggable Authentication Modules • Shared Library shimming • The vulnerability • The Slimjim code • Demonstration • Conclusions www.shmoo.com/rodney/slimjim.ppt

  3. Disclaimer • We’re not suggesting you do anything bad with this. • This is for academic research purposes only. www.shmoo.com/rodney/slimjim.ppt

  4. ‘Slimjim’ – a shared library shim • Takes advantage of shared library technology • Used to intercept data flowing to PAM • Can be applied to OpenSSH + PAM • Extracts passwords www.shmoo.com/rodney/slimjim.ppt

  5. Shared Library Plumbing Conventional SSH+PAM configuration OpenSSH PAM www.shmoo.com/rodney/slimjim.ppt

  6. Shared Library Plumbing Exploited SSH+PAM configuration OpenSSH Slimjim PAM Slimjim captures function calls across Shared Library interface www.shmoo.com/rodney/slimjim.ppt

  7. PAM • Pluggable Authentication Modules • Uses shared libraries to implement access control • Supports password access and other mechanisms • Used by many components, including OpenSSH, ‘su’, ‘telnet’, login, … www.shmoo.com/rodney/slimjim.ppt

  8. Shared Library Shimming Shared Library Public function Well known public functions published by shared library, so interfaces are known Public function Public function www.shmoo.com/rodney/slimjim.ppt

  9. Shimming a shared library • Write a new shared library • Publish the same interfaces by name • At initialization, call the old library • ‘sift’ the data as it passes through • Since the interfaces are the same, theusing program won’t know www.shmoo.com/rodney/slimjim.ppt

  10. The Vulnerability • PAM provides password authentication • PAM uses shared libraries • OpenSSH on Linux uses PAM • OpenSSH doesn’t know which ‘PAM’ it’s using • No security on library loading. www.shmoo.com/rodney/slimjim.ppt

  11. Slimjim Implementation • Source code at http://www.shmoo.com/rodney/slimjim.tgz • Tested with Red Hat 9,OpenSSH 3.6p1,PAM www.shmoo.com/rodney/slimjim.ppt

  12. The Slimjim code • One file, slimjim.c • Publishes standard PAM entry points: pam_authenticate, pam_start, pam_get_user, ... • Note it implements the ‘conversation’ function www.shmoo.com/rodney/slimjim.ppt

  13. PAM Password Exploit • PAM uses a ‘conversation’ function to pass the username and password from the user to PAM • The data passes across the public shared library interface • Therefore, slimjim sees the password, in the clear www.shmoo.com/rodney/slimjim.ppt

  14. Demonstration • OpenSSH on Port 8022 • Shimmed PAM • Red Hat 9 www.shmoo.com/rodney/slimjim.ppt

  15. Conclusions • Is this a realistic problem? Yes. Attackers can drop files on a system, as ‘root’ • How do you prevent this? Usestaticlibraries • Are shared libraries a good idea? Maybenot. • Implement digitally signed shared library loading? www.shmoo.com/rodney/slimjim.ppt

  16. Thank You! Rodney Thayer rodney@shmoo.com http://www.shmoo.com/rodney/slimjim.html www.shmoo.com/rodney/slimjim.ppt

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