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TLS V1.2 Sigalgs Remote Crash (CVE-2015-0291)
Posted on 12:14 PM by Tina
OpenSSL 1.0.2a fix several security issues, one of them let crash TLSv1.2 based services remotelly from internet.
Regarding to the TLSv1.2 RFC, this version of TLS provides a "signature_algorithms" extension for the client_hello.
Regarding to the TLSv1.2 RFC, this version of TLS provides a "signature_algorithms" extension for the client_hello.
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| Data Structures |
If a bad signature is sent after the renegotiation, the structure will be corrupted, becouse structure pointer:
s->c->shared_sigalgs will be NULL, and the number of algorithms:
s->c->shared_sigalgslen will not be zeroed.
Which will be interpreted as one algorithm to process, but the pointer points to 0x00 address.
s->c->shared_sigalgs will be NULL, and the number of algorithms:
s->c->shared_sigalgslen will not be zeroed.
Which will be interpreted as one algorithm to process, but the pointer points to 0x00 address.
Then tls1_process_sigalgs() will try to process one signature algorithm (becouse of shared_sigalgslen=1) then sigptr will be pointer to c->shared_sigalgs (NULL) and then will try to derreference sigptr->rhash.
This mean a Segmentation Fault in tls1_process_sigalgs() function, and called by tls1_set_server_sigalgs() with is called from ssl3_client_hello() as the stack trace shows.
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| StackTrace |
The following code, points sigptr to null and try to read sigptr->rsign, which is assembled as movzbl eax, byte ptr [0x0+R12] note in register window that R12 is 0x00
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| Debugger in the crash point. |
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| radare2 static decompiled |
Get David A. Ramos' proof of concept exploit here
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