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Perl: Format string errors can lead to code execution


1.  Gentoo Linux Security Advisory

Version Information

Advisory Reference GLSA 200512-01 / Perl
Release Date December 07, 2005
Latest Revision December 07, 2005: 01
Impact high
Exploitable remote and local
Package Vulnerable versions Unaffected versions Architecture(s)
dev-lang/perl < 5.8.7-r3 >= 5.8.7-r3, revision >= 5.8.6-r8 All supported architectures

Related bugreports: #114113


A fix is available for Perl to mitigate the effects of format string programming errors, that could otherwise be exploited to execute arbitrary code.

2.  Impact Information


Perl is a stable, cross-platform programming language created by Larry Wall. It contains printf functions that allows construction of strings from format specifiers and parameters, like the C printf functions. A well-known class of vulnerabilities, called format string errors, result of the improper use of the printf functions in C. Perl in itself is vulnerable to a limited form of format string errors through its own sprintf function, especially through wrapper functions that call sprintf (for example the syslog function) and by taking advantage of Perl powerful string expansion features rather than using format string specifiers.


Jack Louis discovered a new way to exploit format string errors in Perl that could lead to the execution of arbitrary code. This is perfomed by causing an integer wrap overflow in the efix variable inside the function Perl_sv_vcatpvfn. The proposed fix closes that specific exploitation vector to mitigate the risk of format string programming errors in Perl. This fix does not remove the need to fix such errors in Perl code.


Perl applications making improper use of printf functions (or derived functions) using untrusted data may be vulnerable to the already-known forms of Perl format string exploits and also to the execution of arbitrary code.

3.  Resolution Information


Fix all misbehaving Perl applications so that they make proper use of the printf and derived Perl functions.


All Perl users should upgrade to the latest version:

Code Listing 3.1: Resolution

# emerge --sync
# emerge --ask --oneshot --verbose dev-lang/perl

4.  References


Page updated December 07, 2005

Summary: This is a Gentoo Linux Security Advisory

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