The PHP development team has released an update for the widely used scripting language that fixes a number of highly serious bugs, according to the project and independent security researchers.
The developers warned that users should update to PHP 4.3.10 immediately, since some of the bugs are relatively easy to exploit.
Stefan Esser of the Hardened PHP Project, which discovered the most serious flaws during development of security add-ons for PHP, said in an advisory the bugs range "from buffer overflows, to information leak vulnerabilities and path truncation vulnerabilities, to safe_mode restriction bypass vulnerabilities".
The most immediately dangerous flaws relate to PHP's variable unserialiser, unserialize (), which can allow attackers to execute malicious code on a system. "A lot of PHP applications expose the easy-to-exploit unserialize() vulnerability to remote attackers," Esser wrote. He noted that the Hardened-PHP patch makes some of the exploits ineffective.
Attackers could make use of some of the other vulnerabilities to retrieve secret data from the "apache" Web server process, bypass security restrictions and gain escalated privileges, Esser said.
Secunia, an independent security research firm based in Denmark, gave the flaws a "highly critical" rating. The PHP update also fixes more than 30 non-critical bugs, PHP developers said. A complete list of changes is available on the PHP website.
PHP is one of the most commonly used scripting languages on the Internet, and is often embedded in HTML pages.
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