Heap-based buffer underflow in the modmul function in sshbn.c in PuTTY before 0.63 allows remote SSH servers to cause a denial of service (crash) and possibly trigger memory corruption or code execution via a crafted DSA signature, which is not properly handled when performing certain bit-shifting operations during modular multiplication.
CVSS Severity (version 2.0):
Impact Subscore: 6.4
Exploitability Subscore: 8.6
CVSS Version 2 Metrics:
Access Vector: Network exploitable
Access Complexity: Medium
Authentication: Not required to exploit
Impact Type: Allows unauthorized disclosure of information; Allows unauthorized modification; Allows disruption of service
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[oss-security] 20130806 CVE request: three additional flaws fixed in putty 0.63