What is CVE-2024-21591?

CVE-2024-21591 is a critical-severity vulnerability in Juniper Junos, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2024-01-12.

How severe is CVE-2024-21591?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2024-21591 known to be exploited?

3 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Buffer overflow in Juniper Junos

CVE-2024-21591

An Out-of-bounds Write vulnerability in J-Web of Juniper Networks Junos OS on SRX Series and EX Series allows an unauthenticated, network-based attacker to cause a Denial of Service (DoS), or Remote Code Execution (RCE) and obtain root privileges on the device. This issue is caused by use of an insecure function allowing an attacker to overwrite arbitrary memory. This issue affects Juniper Networks Junos OS SRX Series and EX Series: * Junos OS versions earlier than 20.4R3-S9; * Junos OS 21.2 versions earlier than 21.2R3-S7; * Junos OS 21.3 versions earlier than 21.3R3-S5; * Junos OS 21.4 versions earlier than 21.4R3-S5; * Junos OS 22.1 versions earlier than 22.1R3-S4; * Junos OS 22.2 versions earlier than 22.2R3-S3; * Junos OS 22.3 versions earlier than 22.3R3-S2; * Junos OS 22.4 versions earlier than 22.4R2-S2, 22.4R3.

Vulnerability class: Buffer Overflow

Published 2024-01-12 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.175 (97.0th percentile), scored 2026-09-28.

Moderate probability of exploitation in the next 30 days — watch for active exploitation reports. 97th percentile — 97.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.177 · newest: 0.175 · change: -0.001

Affected products

Juniper Junos — versions 20.4, 21.2, 21.3
Juniper Networks Junos OS — versions 0, 21.2, 21.3

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

Public proof-of-concept exploits

References

supportportal.juniper.net/JSA75729 (vendor-advisory, Vendor Advisory)
www.first.org/cvss/calculator/4.0 (technical-description, Third Party Advisory)
curesec.com/blog/article/CVE-2024-21591_Juniper_Remote_Code_Exec.html (Exploit, Third Party Advisory, third-party-advisory)

Frequently asked questions

What is CVE-2024-21591?: CVE-2024-21591 is a critical-severity vulnerability in Juniper Junos, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2024-01-12.
How severe is CVE-2024-21591?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2024-21591 known to be exploited?: 3 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.