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Actively exploited vulnerability

PEAR Archive_Tar: code execution flaw under attack

CVE-2020-28949 · PEAR Archive_Tar Deserialization of Untrusted Data Vulnerability

Business software7.8 high

What is affected

PEAR Archive_Tar is mostly run by companies, schools and public bodies, not on home computers. You are unlikely to have it yourself, but organisations that hold your data may. Breaches that start with flaws like this one are how personal data ends up leaked.

PEAR Archive_Tar allows an unserialization attack because phar: is blocked but PHAR: is not blocked. PEAR stands for PHP Extension and Application Repository and it is an open-source framework and distribution system for reusable PHP components with known usage in third-party products such as Drupal Core and Red Hat Linux.

CISA's description

What an attacker can do

This is a code execution flaw. It lets an attacker run their own commands or programs on the affected system. In practice that usually means taking it over: installing malware, stealing data or using it to reach other devices on the same network.

How it is reached
Needs access to the device or a file opened on it
Access the attacker needs
No account needed
Does the victim have to do something?
Yes, the victim must open or click something

What to do

  1. At home: nothing to install. Keep your own devices updated and use a different password for every service, so that a breach at one organisation does not open your other accounts.
  2. If you administer PEAR Archive_Tar at work: apply the vendor's fix or mitigation now and review logs for signs of compromise, because the flaw was being exploited before it was listed.
  3. If the product is past its support date and no fix exists, take it off the internet or retire it.

Apply updates per vendor instructions.

Action required by CISA for US federal agencies

Vendor advisories and fixes

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on August 25, 2022, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by September 15, 2022, a deadline that has already passed. That deadline does not bind anyone else, but it shows how seriously the agency rates it.

The EPSS model estimates a 85% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 99.7% of all scored vulnerabilities.

Its CVSS severity score is 7.8 out of 10 (high), as recorded in the US National Vulnerability Database.

Technical description

Archive_Tar through 1.4.10 has :// filename sanitization only to address phar attacks, and thus any other stream-wrapper attack (such as file:// to overwrite files) can still succeed.

NIST National Vulnerability Database
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