profile.php in ExtCalendar 2 and earlier allows remote attackers to change the passwords of arbitrary users without providing the original password, and possibly perform other unauthorized actions, via modified values to register.php.

References

• https://nvd.nist.gov/vuln/detail/CVE-2007-0681
• https://exchange.xforce.ibmcloud.com/vulnerabilities/32035
• https://www.exploit-db.com/exploits/3239
• http://osvdb.org/38130