The (1) ssh2_load_userkey and (2) ssh2_save_userkey functions in PuTTY 0.51 through 0.63 do not properly wipe SSH-2 private keys from memory, which allows local users to obtain sensitive information by reading the memory.

MATTA-2015-002

Florent Daigniere discovered that PuTTY did not enforce an acceptable range for the Diffie-Hellman server value, as required by RFC 4253, potentially allowing an eavesdroppable connection to be established in the event of a server weakness.

#779488 CVE-2015-2157

Patrick Coleman discovered that PuTTY did not clear SSH-2 private key information from memory when loading and saving key files, which could result in disclosure of private key material.

-- Colin Watson [cjwatson@debian.org]

NOTE: Tenable Network Security has extracted the preceding description block directly from the DLA security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

Fixed an issue when private keys weren't scrub from memory after use.

Note that Tenable Network Security has extracted the preceding description block directly from the Fedora security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

Patrick Coleman discovered that the Putty SSH client failed to wipe out unused sensitive memory.

In addition Florent Daigniere discovered that exponential values in Diffie Hellman exchanges were insufficienty restricted.

The SSH Terminal emulator putty was updated to the new upstream release 0.64, fixing security issues and bugs :

Security fix: PuTTY no longer retains the private half of users' keys in memory by mistake after authenticating with them. [bsc#920167] (CVE-2015-2157)

New feature: Support for SSH connection sharing, so that multiple instances of PuTTY to the same host can share a single SSH connection instead of all having to log in independently.

Bug fix: IPv6 literals are handled sensibly throughout the suite, if you enclose them in square brackets to prevent the colons being mistaken for a :port suffix.

The remote host has a version of PuTTY installed that is prior to 0.64. It is, therefore, affected by multiple vulnerabilities :

  - An information disclosure vulnerability exists due to a     failure to clear SSH-2 private key information from the     memory during the saving or loading of key files to     disk. A local attacker can exploit this to disclose     potentially sensitive information. (CVE-2015-2157)

  - An information disclose vulnerability exists in the     Diffie-Hellman Key Exchange due to a failure to properly     handle 0 value keys sent by the server. A     man-in-the-middle attacker can exploit this to disclose     potentially sensitive information.

Simon Tatham reports :

When PuTTY has sensitive data in memory and has no further need for it, it should wipe the data out of its memory, in case malware later gains access to the PuTTY process or the memory is swapped out to disk or written into a crash dump file. An obvious example of this is the password typed during SSH login; other examples include obsolete session keys, public-key passphrases, and the private halves of public keys.

PuTTY 0.63 and earlier versions, after loading a private key from a disk file, mistakenly leak a memory buffer containing a copy of the private key, in the function ssh2_load_userkey. The companion function ssh2_save_userkey (only called by PuTTYgen) can also leak a copy, but only in the case where the file it tried to save to could not be created.

ID	Name	Product	Family	Severity
82158	Debian DLA-173-1 : putty security update	Nessus	Debian Local Security Checks	low
81854	Fedora 20 : putty-0.64-1.fc20 (2015-3204)	Nessus	Fedora Local Security Checks	low
81853	Fedora 21 : putty-0.64-1.fc21 (2015-3160)	Nessus	Fedora Local Security Checks	low
81849	Fedora 22 : putty-0.64-1.fc22 (2015-3070)	Nessus	Fedora Local Security Checks	low
81834	Debian DSA-3190-1 : putty - security update	Nessus	Debian Local Security Checks	low
81762	openSUSE Security Update : putty (openSUSE-2015-218)	Nessus	SuSE Local Security Checks	low
81669	PuTTY < 0.64 Multiple Information Disclosure Vulnerabilities	Nessus	Windows	medium
81659	FreeBSD : PuTTY -- fails to scrub private keys from memory after use (92fc2e2b-c383-11e4-8ef7-080027ef73ec)	Nessus	FreeBSD Local Security Checks	low

Detections

Analytics

CVE-2015-2157

medium

Tenable Plugins

low

low

low

low

low

low

medium

low