CVE-2021-21708: UAF due to php_filter_float() failing

Published Feb 14, 2022
·
Updated

Fix #81708: UAF due to phpfilterfloat() failing for ints. (CVE-2021-21708)

Other sources

In PHP versions 7.4.x below 7.4.28, 8.0.x below 8.0.16, and 8.1.x below 8.1.3, when using filter functions with FILTERVALIDATEFLOAT filter and min/max limits, if the filter fails, there is a possibility to trigger use of allocated memory after free, which can result it crashes, and potentially in overwrite of other memory chunks and RCE. This issue affects: code that uses FILTERVALIDATEFLOAT with min/max limits.

Use after free due to phpfilterfloat() failing for ints.

References:

https://bugs.php.net/bug.php?id=81708 https://www.php.net/ChangeLog-7.php

— Red Hat

Affected Software

11 affected componentsFixes available
debian/php7.3
7.3.31-1~deb10u17.3.31-1~deb10u5
debian/php7.4
7.4.33-1+deb11u4
PHP PHP>=7.4.0<7.4.28
PHP PHP>=8.0.0<8.0.16
PHP PHP>=8.1.0<8.1.3
PHP PHP<8.1.3
8.1.3
Microsoft cbl2 php
Patch available
alpine/php7<7.4.32-r0
7.4.32-r0
alpine/php7<7.4.28-r0
7.4.28-r0
alpine/php8<8.0.16-r0
8.0.16-r0
redhat/php<7.4.28
7.4.28

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade debian/php7.3 to a version that resolves this vulnerability.

    Fixed in 7.3.31-1~deb10u1Fixed in 7.3.31-1~deb10u5
  2. Upgrade

    Upgrade debian/php7.4 to a version that resolves this vulnerability.

    Fixed in 7.4.33-1+deb11u4
  3. Upgrade

    Upgrade PHP to a version that resolves this vulnerability.

    Fixed in 8.1.3
  4. Upgrade

    Upgrade alpine/php7 to a version that resolves this vulnerability.

    Fixed in 7.4.32-r0
  5. Upgrade

    Upgrade alpine/php7 to a version that resolves this vulnerability.

    Fixed in 7.4.28-r0
  6. Upgrade

    Upgrade alpine/php8 to a version that resolves this vulnerability.

    Fixed in 8.0.16-r0
  7. Upgrade

    Upgrade redhat/php to a version that resolves this vulnerability.

    Fixed in 7.4.28
  8. Upgrade

    Upgrade PHP to a version that resolves this vulnerability.

    Fixed in 7.4.28
  9. Upgrade

    Upgrade PHP to a version that resolves this vulnerability.

    Fixed in 8.0.16

Event History

Feb 17, 2022
CVE Published
via PHP·12:00 AM
Data Sourced
via Red Hat·08:43 PM
DescriptionSeverityAffected Software
Feb 27, 2022
CVE Published
via MITRE·08:00 AM
Data Sourced
via MITRE·08:00 AM
DescriptionSeverityWeakness
Data Sourced
via OSV·08:15 AM
DescriptionSeverityAffected Software
Oct 1, 2025
Data Sourced
via Microsoft·11:11 PM
DescriptionSeverityWeakness
Data Sourced
via Microsoft·11:11 PM
Affected Software

Frequently Asked Questions

1

What is CVE-2021-21708?

CVE-2021-21708 is a vulnerability in PHP that allows for a use-after-free (UAF) issue due to php_filter_float() failing for ints.

2

How severe is CVE-2021-21708?

CVE-2021-21708 is considered a moderate severity vulnerability.

3

Which version of PHP is affected by CVE-2021-21708?

Versions of PHP up to and excluding 7.4.28 are affected by CVE-2021-21708.

4

How can I fix CVE-2021-21708?

To fix CVE-2021-21708, upgrade to PHP version 7.4.28 or apply the necessary patches as provided by the PHP project.

5

Where can I find more information about CVE-2021-21708?

More information about CVE-2021-21708 can be found in the PHP changelog at https://www.php.net/ChangeLog-7.php#7.4.28.

Company

Resources

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