Buffer overflow in Juniper Junos
CVE-2026-21903
A Stack-based Buffer Overflow vulnerability in the Packet Forwarding Engine (pfe) of Juniper Networks Junos OS allows a network-based attacker, authenticated with low privileges to cause a Denial-of-Service (DoS). Subscribing to telemetry sensors at scale causes all FPC connections to drop, resulting in an FPC crash and restart. The issue was not seen when YANG packages for the specific sensors were installed. This issue affects Junos OS: * all versions before 22.4R3-S7, * 23.2 version before 23.2R2-S4, * 23.4 versions before 23.4R2.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.004 (32.3th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 32nd percentile — 32.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: +0.000
Affected products
- Juniper Junos — versions 22.4, 23.2, 23.4
- Juniper Networks Junos OS — versions 0, 23.2, 23.4
Weakness classification (CWE)
References
- supportportal.juniper.net/JSA106022 (vendor-advisory, Vendor Advisory)
- kb.juniper.net/JSA106022 (vendor-advisory, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-21903?
- CVE-2026-21903 is a medium-severity vulnerability in Juniper Junos, classified under Stack-based Buffer Overflow. CVSS score: 6.5/10. Published 2026-01-15.
- How severe is CVE-2026-21903?
- Medium severity. CVSS v3 base score is 6.5 out of 10.