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CVE-2017-3737

Published: 07 December 2017

OpenSSL 1.0.2 (starting from version 1.0.2b) introduced an "error state" mechanism. The intent was that if a fatal error occurred during a handshake then OpenSSL would move into the error state and would immediately fail if you attempted to continue the handshake. This works as designed for the explicit handshake functions (SSL_do_handshake(), SSL_accept() and SSL_connect()), however due to a bug it does not work correctly if SSL_read() or SSL_write() is called directly. In that scenario, if the handshake fails then a fatal error will be returned in the initial function call. If SSL_read()/SSL_write() is subsequently called by the application for the same SSL object then it will succeed and the data is passed without being decrypted/encrypted directly from the SSL/TLS record layer. In order to exploit this issue an application bug would have to be present that resulted in a call to SSL_read()/SSL_write() being issued after having already received a fatal error. OpenSSL version 1.0.2b-1.0.2m are affected. Fixed in OpenSSL 1.0.2n. OpenSSL 1.1.0 is not affected.

Priority

Medium

CVSS 3 base score: 5.9

Status

Package Release Status
openssl
Launchpad, Ubuntu, Debian
Upstream Needs triage

Ubuntu 16.04 ESM (Xenial Xerus)
Released (1.0.2g-1ubuntu4.10)
Ubuntu 14.04 ESM (Trusty Tahr) Not vulnerable
(code not present)
Patches:
Upstream: https://git.openssl.org/?p=openssl.git;a=commit;h=898fb884b706aaeb283de4812340bb0bde8476dc
Upstream: https://git.openssl.org/?p=openssl.git;a=commit;h=c7383fb5f21aa3451f76bb98bdd5a96b070a2c47 (test)

Notes

AuthorNote
leosilva
this issue does not affect OpenSSL 1.1.0
mdeslaur
1.0.2b introduced a security hardening mechanism designed to
protect against bugs in application code.
https://git.openssl.org/?p=openssl.git;a=commit;h=e4f77bf1833245d2b6aa4ce6a16c85e1cdf78589
This CVE applies to the hardening mechanism being incomplete.
openssl versions older than 1.0.2b don't have the hardening
mechanism at all.

References