putty: multiple vulnerabilities
|Created:||August 12, 2013
||Updated:||September 30, 2013|
||From the Debian advisory:
Mark Wooding discovered a heap-corrupting buffer underrun bug in the
modmul function which performs modular multiplication. As the modmul
function is called during validation of any DSA signature received
by PuTTY, including during the initial key exchange phase, a
malicious server could exploit this vulnerability before the client
has received and verified a host key signature. An attack to this
vulnerability can thus be performed by a man-in-the-middle between
the SSH client and server, and the normal host key protections
against man-in-the-middle attacks are bypassed.
It was discovered that non-coprime values in DSA signatures can
cause a buffer overflow in the calculation code of modular inverses
when verifying a DSA signature. Such a signature is invalid. This
bug however applies to any DSA signature received by PuTTY,
including during the initial key exchange phase and thus it can be
exploited by a malicious server before the client has received and
verified a host key signature.
It was discovered that private keys were left in memory after being
used by PuTTY tools.
Gergely Eberhardt from SEARCH-LAB Ltd. discovered that PuTTY is
vulnerable to an integer overflow leading to heap overflow during
the SSH handshake before authentication due to improper bounds
checking of the length parameter received from the SSH server. A
remote attacker could use this vulnerability to mount a local denial
of service attack by crashing the putty client.
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