CVE-2026-0300
CVE-2026-0300 is a security flaw in Palo Alto Networks PAN-OS, the operating system on Palo Alto Networks’ firewalls. Attackers can run their own code on Palo Alto Networks PAN-OS 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 6 May 2026.[1]
Palo Alto Networks PAN-OS 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 12.1.7, 11.2.12, 11.1.15 and 10.2.18-h6 of PAN-OS.
Description
CISA calls it an out-of-bounds write in Palo Alto Networks PAN-OS. In its words: “Palo Alto Networks PAN-OS contains an out-of-bounds write vulnerability in the User-ID Authentication Portal (aka Captive Portal) service that can allow an unauthenticated attacker to execute arbitrary code with root privileges on the PA-Series and VM-Series firewalls by sending specially crafted packets.”[1]
The CVE record adds: “A buffer overflow vulnerability in the User-ID™ Authentication Portal (aka Captive Portal) service of Palo Alto Networks PAN-OS software allows an unauthenticated attacker to execute arbitrary code with root privileges on the PA-Series and VM-Series firewalls by sending specially crafted packets. The risk of this issue is greatly reduced if you secure access to the User-ID™ Authentication Portal per the best practice guidelines https://knowledgebase.paloaltonetworks.com/KCSArticleDetail by restricting access to only trusted internal IP addresses. Prisma Access, Cloud NGFW and Panorama appliances are not impacted by this vulnerability.”[2]
The underlying weakness is out-of-bounds write (CWE-787), 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 |
|---|---|
| PAN-OS | 12.1.7 |
| PAN-OS | 11.2.12 |
| PAN-OS | 11.1.15 |
| PAN-OS | 10.2.18-h6 |
Most families won’t have Palo Alto Networks PAN-OS; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 6 May 2026, within a day of it being made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 9 May 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 42%. That’s in the top 2% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
Palo Alto Networks has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.”[1]
- Check whether you use it.Palo Alto Networks PAN-OS 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 12.1.7, 11.2.12, 11.1.15 and 10.2.18-h6 of PAN-OS), or not in use. CISA gave US government agencies until 9 May 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 42%.[4] |
See also
Other Palo Alto Networks PAN-OS flaws
- CVE-2026-0322: code injection ·
- CVE-2026-0257: authentication bypass ·
- CVE-2025-0111: file read ·
- CVE-2025-0108: authentication bypass ·
- CVE-2024-3393: malicious DNS packet ·
- CVE-2024-9474: management interface OS command injection ·
Other Palo Alto Networks flaws
- CVE-2024-9465, Palo Alto Networks Expedition: SQL injection ·
- CVE-2024-9463, Palo Alto Networks Expedition: OS command injection ·
- CVE-2024-5910, Palo Alto Networks Expedition: missing authentication ·
Other out-of-bounds write flaws
- CVE-2026-86950, Apple devices: out-of-bounds write ·
- CVE-2026-53266, Linux Kernel: out-of-bounds write ·
- CVE-2026-87491, Chrome and other Chromium browsers: out of bounds write ·
- CVE-2026-53362, Linux Kernel: unspecified ·
- CVE-2022-0995, Linux Kernel: out-of-bounds write ·
Every Palo Alto Networks flaw on CISA’s list · Everything added in May 2026
References
- ^ Cybersecurity and Infrastructure Security Agency. “Palo Alto Networks PAN-OS Out-of-bounds Write Vulnerability”. Known Exploited Vulnerabilities Catalog, added 6 May 2026.
- ^ National Institute of Standards and Technology. “CVE-2026-0300 Detail”. National Vulnerability Database, published 6 May 2026.
- ^ Palo Alto Networks. Advisories and fixes: security.paloaltonetworks.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.417, percentile 98.7, 31 Oct 2026.
- CVE Program. “CVE-2026-0300”. 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.