CVE-2021-4251: A vulnerability classified as problematic was found in as

Q: How do I fix CVE-2021-4251?

as: upgrade to 2021-11-03. Exact commands for each OS are on this page.

Q: Is CVE-2021-4251 being exploited?

CVE-2021-4251 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-4251 affect?

CVE-2021-4251 affects as. Severity is low (CVSS 3.5). A vulnerability classified as problematic was found in as. This vulnerability affects the function getFullURL of the file include.cdn.php. The manipulation leads to cross site scripting. The attack can be initiated remotely. The name of the

Q: How urgent is CVE-2021-4251?

Priority 21/100. No elevated risk signals yet.

Routine

LOW 3.5UPGRADE

CVE-2021-4251 is a low-severity flaw (CVSS 3.5) affecting as. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A vulnerability classified as problematic was found in as. This vulnerability affects the function getFullURL of the file include.cdn.php. The manipulation leads to cross site scripting. The attack can be initiated remotely. The name of the patch is 4acad1e3d2c34c017473ceea442fb3e3e078b2bd. It is recommended to apply a patch to fix this issue. The identifier of this vulnerability is VDB-216208.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	3.5 (Low)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	Required
EPSS exploit chance	0.4% (top 64%)
CISA exploited list	No
Weakness	CWE-707
Published	2022-12-18
Last modified	2026-06-17

Publisher (CNA): VulDB · Vendor: as project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2022-12-18 22:15 UTCPublished CVE record published
2026-06-17 04:19 UTCUpdated Record last modified

as project as UPGRADE

Affected: < 2021-11-03

Fixed in: 2021-11-03

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy as || rpm -q as || as --version

2. UPGRADE to 2021-11-03 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade as

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade as

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-4251?

as: upgrade to 2021-11-03. Exact commands for each OS are on this page.

Is CVE-2021-4251 being exploited?

CVE-2021-4251 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-4251 affect?

CVE-2021-4251 affects as. Severity is low (CVSS 3.5). A vulnerability classified as problematic was found in as. This vulnerability affects the function getFullURL of the file include.cdn.php. The manipulation leads to cross site scripting. The attack can be initiated remotely. The name of the

How urgent is CVE-2021-4251?

Priority 21/100. No elevated risk signals yet.

Software pages

PHP vulnerabilities

References

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