Junos OS: Out-of-bounds write in rpd enables denial of service via BGP update
Summary
A flaw in the routing protocol daemon (rpd) of Junos OS and Junos OS Evolved allows an out-of-bounds write triggered by a malformed BGP update. An attacker who is an eBGP peer that has not negotiated the four-octet AS capability can crash the routing daemon and cause a denial of service. The attack requires an established eBGP session, so routers without their own BGP peers are not exposed this way.
Affected
- Junos OS: before 23.2R2-S7.7; 23.4 to before 23.4R2-S8.13; 24.2 to before 24.2R2-S5.5; 24.4 to before 24.4R2-S5; 25.2 to before 25.2R2-S2; 25.4 to before 25.4R1-S3; 26.2 to before 26.2R1-S2 (default configuration: unaffected)
- Junos OS Evolved: before 23.2R2-S7.7-EVO; 23.4 to before 23.4R2-S8.11-EVO; 24.2 to before 24.2R2-S5.6-EVO; 24.4 to before 24.4R2-S5-EVO; 25.2 to before 25.2R2-S2-EVO; 25.4 to before 25.4R1-S3-EVO; 26.2 to before 26.2R1-S2-EVO; 23.4X100; 25.2X100 to before 25.2X100-D35-EVO; 25.4X300 to before 25.4X300-D40-EVO (default configuration: unaffected)
- Relevant configuration: protocols bgp, neighbor
Fixed in
- Junos OS: 23.2R2-S7.7, 23.4R2-S8.13, 24.2R2-S5.5, 24.4R2-S5, 25.2R2-S2, 25.4R1-S3, 25.4R2, 26.2R1-S2, 26.2R2, 26.4R1 and all subsequent releases
- Junos OS Evolved: 23.2R2-S7.7-EVO, 23.4R2-S8.11-EVO, 24.2R2-S5.6-EVO, 24.4R2-S5-EVO, 25.2R2-S2-EVO, 25.4R1-S3-EVO, 25.4R2-EVO, 26.2R1-S2-EVO, 26.2R2-EVO, 26.4R1-EVO and all subsequent releases
- For 23.2, 23.4 and 24.2 the vendor has published respins; previously published builds of these releases have been rebuilt. Check the exact build in the advisory.
Workaround
No known workarounds.
Exploitation
- Juniper SIRT is not aware of any malicious exploitation.
- Not listed in CISA KEV; no public proof of concept found.
- CISA SSVC: exploitation none, automatable yes, technical impact partial.
Our recommendation
- Inventory all Junos OS and Junos OS Evolved devices and check whether they run BGP sessions, especially eBGP.
- Install the fixed releases from Juniper advisory JSA112187; patch the whole bulletin, not only this CVE.
- Until patching is done, restrict BGP sessions to known and expected peers using session and prefix filters.
- Monitor routing daemon crashes and unexpected BGP session resets.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Juniper Security Advisory JSA112187 supportportal.juniper.net
- CVE record mirror (OpenCVE) CVE-2026-101976 app.opencve.io
- Strix CVE-2026-101976 (republished CNA data) www.strix.ai
- CVSS 4.0 score reference CVE-2026-101976 cve.threatint.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 02:51.
Original description (NVD)
An Out-of-bounds Write vulnerability in the routing protocol daemon (rpd) of Juniper Networks Junos OS and Junos OS Evolved allows an eBGP peer which has not negotiated four-octet-AS capability sending a specifically malformed BGP update to cause a Denial-of-Service (DoS).
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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