CVE-2023-36845
CVE-2023-36845 is a security flaw in Juniper Junos OS, the operating system on Juniper’s routers and firewalls. Attackers can run their own code on Juniper Junos 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 13 Nov 2023.[1]
Juniper Junos 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 20.4R3-S9, 21.1*, 21.2R3-S7 and 21.3R3-S5 and others of Junos OS.
Description
CISA calls it an EX series and SRX series PHP external variable modification in Juniper Junos OS. In its words: “Juniper Junos OS on EX Series and SRX Series contains a PHP external variable modification vulnerability that allows an unauthenticated, network-based attacker to control an important environment variable. Using a crafted request, which sets the variable PHPRC, an attacker is able to modify the PHP execution environment allowing the injection und execution of code.”[1]
The CVE record adds: “A PHP External Variable Modification vulnerability in J-Web of Juniper Networks Junos OS on EX Series and SRX Series allows an unauthenticated, network-based attacker to remotely execute code. Using a crafted request which sets the variable PHPRC an attacker is able to modify the PHP execution environment allowing the injection und execution of code. This issue affects Juniper Networks Junos OS on EX Series and SRX Series: * All versions prior to 20.4R3-S9; * 21.1 versions 21.1R1 and later; * 21.2 versions prior to 21.2R3-S7; * 21.3 versions prior to 21.3R3-S5; * 21.4 versions prior to 21.4R3-S5; * 22.1 versions prior to 22.1R3-S4; * 22.2 versions prior to 22.2R3-S2; * 22.3 versions prior to 22.3R2-S2, 22.3R3-S1; * 22.4 versions prior to 22.4R2-S1, 22.4R3; * 23.2 versions prior to 23.2R1-S1, 23.2R2.”[2]
The underlying weakness is CWE-473, 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 the organisation that published the CVE 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 |
|---|---|
| Junos OS | 20.4R3-S9 |
| Junos OS | 21.1* |
| Junos OS | 21.2R3-S7 |
| Junos OS | 21.3R3-S5 |
| Junos OS | 21.4R3-S5 |
| Junos OS | 22.1R3-S4 |
| Junos OS | 22.2R3-S2 |
| Junos OS | 22.3R2-S2, 22.3R3-S1 |
Most families won’t have Juniper Junos OS; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 13 Nov 2023, 88 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 17 Nov 2023 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 95%. That’s in the top 1% 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
Juniper has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.”[1]
- Check whether you use it.Juniper Junos 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 20.4R3-S9, 21.1*, 21.2R3-S7 and 21.3R3-S5 and others of Junos OS), or not in use. CISA gave US government agencies until 17 Nov 2023 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 95%.[4] |
See also
Other Juniper Junos OS flaws
- CVE-2025-21590: improper isolation or compartmentalization ·
- CVE-2023-36851: SRX series missing authentication for critical function ·
- CVE-2023-36847: EX series missing authentication for critical function ·
- CVE-2023-36846: SRX series missing authentication for critical function ·
- CVE-2023-36844: EX series PHP external variable modification ·
- CVE-2020-1631: path traversal ·
Other Juniper flaws
- CVE-2015-7755, Juniper ScreenOS: improper authentication ·
Added the same day
- CVE-2023-47246, SysAid Server: server path traversal ·
- CVE-2023-36851, Juniper Junos OS: SRX series missing authentication for critical function ·
- CVE-2023-36847, Juniper Junos OS: EX series missing authentication for critical function ·
- CVE-2023-36846, Juniper Junos OS: SRX series missing authentication for critical function ·
- CVE-2023-36844, Juniper Junos OS: EX series PHP external variable modification ·
Every Juniper flaw on CISA’s list · Everything added in November 2023
References
- ^ Cybersecurity and Infrastructure Security Agency. “Juniper Junos OS EX Series and SRX Series PHP External Variable Modification Vulnerability”. Known Exploited Vulnerabilities Catalog, added 13 Nov 2023.
- ^ National Institute of Standards and Technology. “CVE-2023-36845 Detail”. National Vulnerability Database, published 17 Aug 2023.
- ^ Juniper. Advisories and fixes: supportportal.juniper.net, supportportal.juniper.net.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.951, percentile 99.9, 31 Oct 2026.
- CVE Program. “CVE-2023-36845”. 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.