CVE-2017-3737
Publication date 7 December 2017
Last updated 25 August 2025
Ubuntu priority
Description
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.
Status
| Package | Ubuntu Release | Status |
|---|---|---|
| openssl | ||
| 16.04 LTS xenial |
Fixed 1.0.2g-1ubuntu4.10
|
|
| 14.04 LTS trusty |
Not affected
|
Notes
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.
Patch details
| Package | Patch details |
|---|---|
| openssl |
Severity score breakdown
| Parameter | Value |
|---|---|
| Base score |
5.9 · Medium
|
| Attack vector | Network |
| Attack complexity | High |
| Privileges required | None |
| User interaction | None |
| Scope | Unchanged |
| Confidentiality | High |
| Integrity impact | None |
| Availability impact | None |
| Vector | CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N |
References
Related Ubuntu Security Notices (USN)
- USN-3512-1
- OpenSSL vulnerabilities
- 11 December 2017