CVE-2026-109618
CVE-2026-109618 is a security flaw in PHP, the programming language behind many websites. Attackers can run their own code on PHP from anywhere, without logging in. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 26 Oct 2026.[1]
PHP is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fixed in version 8.2.35, 8.3.36, 8.4.27 and 8.5.12 of PHP.
Description
CISA calls it a memory corruption in PHP Group PHP. In its words: “PHP contains an out-of-memory corruption vulnerability that allows for unauthenticated remote code execution.”[1]
The CVE record adds: “PHP uses longjmp() for out-of-memory (OOM) errors to exit the current context and abort handling of the request. Some contexts may not properly account for this scenario and leave request memory in an uninitialized state before performing an allocation. The subsequent request cleanup procedure may read or branch on this memory. Multiple OOM strategies can consistently trigger this condition and lead to remote code execution (RCE).”[2]
The underlying weakness is use after free (CWE-416), CWE-755, CWE-824, in MITRE’s list of common software weaknesses.
It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]
| Product | Fixed in |
|---|---|
| PHP | 8.2.35 |
| PHP | 8.3.36 |
| PHP | 8.4.27 |
| PHP | 8.5.12 |
Most families won’t have PHP; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 26 Oct 2026, 5 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 29 Oct 2026 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at over 99%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
PHP Group has published a fix or advice.[3] CISA’s required action: “Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes).”[1]
- Check whether you use it.PHP is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed (fixed in version 8.2.35, 8.3.36, 8.4.27 and 8.5.12 of PHP), or not in use. CISA gave US government agencies until 29 Oct 2026 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 9.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at over 99%.[4] |
See also
Other PHP flaws
- CVE-2026-109619: stale internal request-state ·
- CVE-2024-4577: PHP-CGI OS command injection ·
Other use after free flaws
- CVE-2026-68820, Microsoft Windows Ancillary Function Driver for WinSock: use-after-free ·
- CVE-2010-0249, Microsoft Internet Explorer: use-after-free ·
- CVE-2020-9715, Adobe Acrobat: use-after-free ·
- CVE-2026-5281, Google Dawn: use-after-free ·
- CVE-2023-43000, Apple devices: use-after-free ·
Added the same day
- CVE-2026-109619, PHP: stale internal request-state ·
Every PHP Group flaw on CISA’s list · Everything added in October 2026
References
- ^ Cybersecurity and Infrastructure Security Agency. “PHP Memory Corruption Vulnerability”. Known Exploited Vulnerabilities Catalog, added 26 Oct 2026.
- ^ National Institute of Standards and Technology. “CVE-2026-109618 Detail”. National Vulnerability Database, published 21 Oct 2026.
- ^ PHP Group. Advisories and fixes: php.net, github.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 1.000, percentile 100.0, 31 Oct 2026.
- CVE Program. “CVE-2026-109618”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.