CVE-2026-63223: CodeIgniter: Uploaded file extension validation bypass in `is_image` and `mime_in` rules

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.8%, percentile 56: FIRST’s model estimates a 0.8% chance of exploitation activity in the next 30 days, higher than 56% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes codeigniter4/framework (Composer (PHP)) < 4.7.4, fixed in 4.7.4. Check your lockfile, including transitive dependencies.

What it is

CodeIgniter is a PHP full-stack web framework. Prior to 4.7.4, the isimage and mimein upload validation rules do not independently enforce a safe client filename extension, allowing a remote attacker to upload executable content when an application preserves the client filename and stores uploads in a web-accessible script-enabled directory. Applications are impacted when they validate uploads using isimage or mimein without an independent safe extension check (such as extin on patched versions), save uploaded files using the client-supplied filename, and place uploads in a web-accessible directory where PHP files can execute. This issue is fixed in version 4.7.4.

From the GitHub advisory

Impact This is an unsafe file upload validation vulnerability that can lead to remote code execution in vulnerable application configurations.

Applications are impacted when they: - validate uploads using isimage or mimein without an independent safe extension check, such as extin on patched versions - save uploaded files using the client-supplied filename - place uploads in a web-accessible directory where PHP files can execute

Patches Upgrade to v4.7.4 or later.

Workarounds - Save uploads outside the public web root, preferably under writable/uploads. - Use $file->store() or $file->move($path, $file->getRandomName()) instead of preserving the original client filename. - Disable script execution in any public upload directory. - Manually verify the client filename extension before moving the file. - For image uploads, reject files when $file->getClientExtension() is not an allowed image extension. - For exact MIME-type validation, reject files when $file->getClientExtension() does not match $file->guessExtension().

Weakness type: CWE-434.

Product: codeigniter4/framework (Composer (PHP)) · Assigned by: GitHub_M · Published: 2026-07-31

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.80% probability of exploitation activity in the next 30 days; percentile 56.

Timeline

• 2026-07-31 — CVE record last updated
• 2026-07-31 — CVE record published by GitHub_M
• 2026-08-07 — GitHub-reviewed advisory GHSA-mmj4-63m4-r6h5 published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-mmj4-63m4-r6h5 github.com
2. CVE.org record CVE-2026-63223 cve.org
3. NVD entry CVE-2026-63223 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

Critical Composer (PHP) advisories · Today’s Security Digest