Bug 645859 (CVE-2010-4051, CVE-2010-4052)

Maksymilian Arciemowicz reported a deficiency in the way
glibc regular expression engine processed certain patterns.
A local attacker could use this flaw to cause a denial of 
service (crash due stack overflow).

Note: The above described behavior is a limitation of glibc
regular expression engine. Regular expression matching 
function is called recursively for certain types of patterns 
(where subexpression using quantifier is nested inside of 
another quantified expression), where long input can result 
in deep recursion and exhaustion of all stack memory (i.e. 
impact is limited to crash). Amount of stack memory available
to glibc regular expression engine influences the size of input 
that must be provided to trigger the crash. Alternatively, 
expression can be modified to avoid quantification nesting, 
or program modified to limit size of input passed to regular
expression engine.

Conclusion: Due the above described behavior Red Hat Security
Response Team would not classify this deficiency to be a security
issue.

References:
[1] http://www.kb.cert.org/vuls/id/912279
[2] http://www.securityfocus.com/archive/1/515589
[3] http://forums.cnet.com/7726-6132_102-5042238.html
[4] http://secunia.com/advisories/42547/
[5] http://securityreason.com/securityalert/8003