Atlassian Crowd 2.6.3 allows remote attackers to execute arbitrary commands via unspecified vectors related to a "symmetric backdoor." NOTE: as of 20130704, the vendor could not reproduce the issue, stating "We've been unable to substantiate the existence of [CVE-2013-3926]. The author of the article has not contacted Atlassian and has provided no detail, making it difficult to validate the claim... If we can confirm that there is a vulnerability, a patch will be issued.