What is CVE-2026-109618?A critical-severity flaw criminals are using now.
CVE-2026-109618 is a critical-severity flaw (CVSS 9.2) in the software it affects, published on 20 October 2026. It is on the list of flaws known to be exploited, so criminals are already using it. The latest forecast puts its chance of use in the next 30 days at over 99%. If you run an affected version, patch it first.
Published 20 October 2026. Record last updated 21 October 2026. We keep this page's data up to date.
What is CVE-2026-109618? In plain terms.
Here is what the published record says about this flaw, and what kind of weakness it is.
Unauthenticated remote code execution vulnerability in PHP core, the first of two flaws known as "php2shell". watchTowr reported reproducing this vulnerability in a lab. The PHP security team rates it critical (CVSS v4.0 9.2) and scheduled an out-of-band security release for 21 October 2026 at 14:00 UTC, which publishes the affected and fixed versions; CERT-EU (Security Advisory 2026-018) warns that all PHP versions from PHP 5 onwards could be affected. Details leaked on 20 October 2026, about 15:20 UTC, ahead of a coordinated disclosure planned for later that week, and the PHP team brought its release forward. There are reports of exploitation in the wild, not yet confirmed by the PHP security team or listed by CISA. There are also reports of a leaked exploit tool called "PHP2Shell" said to work against every release from PHP 5.4.0, and researchers expect mass exploitation soon after the patch is published. The root cause has not been published by PHP. An unverified write-up circulating with a proof-of-concept bundle attributes the php2shell flaws to heap use-after-free bugs in the session extension's upload progress handler (session.upload_progress, php_session_rfc1867_callback) and in the multipart/form-data parser, so any multipart POST to a PHP endpoint may reach the vulnerable code.
How an attack on it works
Read straight from its severity rating, translated out of the shorthand.
This record has no severity breakdown yet.
Is CVE-2026-109618 being exploited? Yes.
Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at over 99%.
Timeline
- Published
- Record last updated
- Exploit likelihood jumped
- Added to the known-exploited list
CVE-2026-109618 scores 89. Action: Emergency patch.
We keep the score of every published flaw up to date as the evidence changes. Four things go into the score, and evidence that criminals are actually using it counts most. In order:
- Evidence it is being exploitedBiggest factor
- How severe it isStrong factor
- How widely exposed it isKey context
- Real threat activity around itKey context
85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score.
When CVE-2026-109618 matches software you track, it lands in your list with its score and the reasons behind it.
See your own ranked list →Who is affected by CVE-2026-109618? 0 products.
Here is what the published record lists as affected.
No affected products have been listed for this flaw yet. That usually means the record is still being analysed.
How do I fix CVE-2026-109618? Four steps.
- Check whether you run itCompare your versions with the affected products above. Not sure what you run? EdgeProtect can work it out from your public website, or you can pick it from a list.
- Apply the vendor’s fixInstall the update named in the vendor’s advisory. We’ve put the advisories and patch notes first in the list.
- If you can’t patch todayFollow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
- Check it wasn’t used before you patchedBecause criminals are already using this flaw, look for signs of a break-in on affected systems using the vendor’s guidance.
References
9 links- Web page (opens in a new tab)php.net
- Supported Versions (opens in a new tab)php.net
- Php2shell Leaked Critical Php Vulnerabilities (opens in a new tab)huntress.com
- Neo23x0/process-watcher file (opens in a new tab)github.com
- Advisory for CVE-2026-109618 (opens in a new tab)watchtowr.com
- Php Warns Admins of Two Critical Flaws Emergency Patches Coming Tomorrow (opens in a new tab)bleepingcomputer.com
Does CVE-2026-109618 affect you? We'll keep checking.
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1 flaw being exploited affects software Acme tracks
Unauthenticated remote code execution vulnerability in PHP core, the first of two flaws known as "php2shell". watchTowr reported reproducing this vulnerabili...
- Matched to
- Your software on Acme's software list
- What to do
- Patch first, then check for signs of use
Sent to the alert recipients Acme chose. Also in the app and to Acme's webhook.
CVE-2026-109618 is a critical-severity flaw in the software it affects, published on 20 October 2026. Here is what the published record says about this flaw, and what kind of weakness it is.
It scores 9.2 out of 10 on the CVSS severity scale, which is critical. Our risk score for CVE-2026-109618 is 89 out of 100, which is Critical. Its action is "Emergency patch". Attackers are using this flaw today. If you run an affected version, it goes to the top of your list.
Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at over 99%.
Install the update the vendor names in its advisory, linked first under "How do I fix" on this page. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet. Because criminals are already using it, also check affected systems for signs of a break-in.