It was discovered that php-json-ext, a JSON serialiser for PHP, is prone to a denial of service attack, when receiving a malformed string via the json_decode function.
For the oldstable distribution (etch), this problem has been fixed in version 1.2.1-3.2+etch1.
The stable distribution (lenny) does not contain a separate php-json-ext package, but includes it in the php5 packages, which will be fixed soon.
The testing distribution (squeeze) and the unstable distribution (sid) do not contain a separate php-json-ext package, but include it in the php5 packages.
We recommend that you upgrade your php-json-ext packages.
MD5 checksums of the listed files are available in the original advisory.