CVE-2021-31374Network attack vector

Routing service interruption via out-of-bounds write

Published Oct 19, 2021 · Updated Sep 16, 2024

Out-of-bounds write in Juniper Networks Junos OS and Junos OS Evolved allows remote attackers to crash and restart RPD via crafted BGP messages. RPD writes beyond a buffer boundary while parsing a specially crafted BGP UPDATE or KEEPALIVE message; Juniper has not disclosed the affected routine. Reachability to an IBGP or EBGP session over IPv4 or IPv6 is sufficient, and repeated messages sustain the routing-service interruption.

CVSS severity7.5
High
EPSS probability1.02%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds write in Juniper Networks Junos OS and Junos OS Evolved allows remote attackers to crash and restart RPD via crafted BGP messages. RPD writes beyond a buffer boundary while parsing a specially crafted BGP UPDATE or KEEPALIVE message; Juniper has not disclosed the affected routine. Reachability to an IBGP or EBGP session over IPv4 or IPv6 is sufficient, and repeated messages sustain the routing-service interruption.

The record

CVE
CVE-2021-31374
Published
Oct 19, 2021
Updated
Sep 16, 2024
Vendor
Juniper Networks
Product
Junos OS Evolved
Classifications
CWE-787, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 19, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=20.3 <20.3R2-EVO

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OS Evolvedversion=20.3 <20.3R2-EVO
Juniper Networks · Junos OSversion=17.3 <17.3R3-S11; version=17.4 <17.4R2-S13, 17.4R3-S4; version=18.1 <18.1R3-S12; version=18.2 <18.2R2-S8, 18.2R3-S7; version=18.3 <18.3R3-S4; version=18.4 <18.4R1-S8, 18.4R2-S7, 18.4R3-S7; version=19.1 <19.1R1-S6, 19.1R2-S2, 19.1R3-S4; version=19.2 <19.2R1-S6, 19.2R3-S1; version=19.3 <19.3R2-S5, 19.3R3-S1; version=19.4 <19.4R1-S4, 19.4R2-S3, 19.4R3-S1; version=20.1 <20.1R2; version=20.2 <20.2R2; version=20.3 <20.3R1-S1, 20.3R2

Published CVSS scores

7.5Juniper NetworksCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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