JunosOperating system · Juniper

CVE-2025-21597

MEDIUM · 5.3 CVSS v3.1 Published 2025-04-09

Fix available

A fix is available. Upgrade to 20.4 / 21.2 or later.

See remediation →

58/100

Remediation priority · Elevated

No privileges Zero-click

Official description

NVD · unedited

An Improper Check for Unusual or Exceptional Conditions vulnerability in routing protocol daemon (rpd) of Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated, logically adjacent BGP peer to cause Denial of Service (DoS). On all Junos OS and Junos OS Evolved platforms, when BGP rib-sharding and update-threading are configured, and a BGP peer flap is done with specific timing, rpd crashes and restarts. Continuous peer flapping at specific time intervals will result in a sustained Denial of Service (DoS) condition. This issue affects eBGP and iBGP, in both IPv4 and IPv6 implementations. This issue requires a remote attacker to have at least one established BGP session. The issue can occur with or without logical-systems enabled. This issue affects: Junos OS: * All versions before 20.4R3-S8, * 21.2 versions before 21.2R3-S6, * 21.3 versions before 21.3R3-S5, * 21.4 versions before 21.4R3-S4, * 22.1 versions before 22.1R3-S3, * 22.2 versions before 22.2R3-S1, * 22.3 versions before 22.3R3, * 22.4 versions before 22.4R3. Junos OS Evolved: * All versions before 21.2R3-S6-EVO, * 21.3-EVO versions before 21.3R3-S5-EVO, * 21.4-EVO versions before 21.4R3-S4-EVO, * 22.1-EVO versions before 22.1R3-S3-EVO, * 22.2-EVO versions before :22.2R3-S1-EVO, * 22.3-EVO versions before 22.3R3-EVO, * 22.4-EVO versions before 22.4R3-EVO.

Technical summary

dbcve analysis · high confidence

A race condition in the routing protocol daemon (rpd) of Juniper Networks Junos OS causes a crash when BGP peer flapping occurs while rib-sharding and update-threading are configured. An attacker with an established BGP session can trigger repeated crashes by flapping the peer at specific time intervals, resulting in sustained denial of service.

MitigationUpgrade Junos OS/Evolved to a patched version listed in the advisory and consider disabling rib-sharding or update-threading as a temporary mitigation if upgrading is not immediately feasible.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions

NVD · CPE data

JunosOperating system

Affected:< 20.4= 20.4= 21.2= 21.3= 21.4= 22.1= 22.2= 22.3= 22.4

Junos Os EvolvedOperating system

Affected:< 21.2= 21.2= 21.3= 21.4= 22.1= 22.2= 22.3= 22.4

CVSS breakdown

From the vector

Attack vector: Adjacent
Complexity: High
Privileges: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected?

dbcve checks

Work through these to decide whether this CVE applies to you.

Check Junos OS version

Run 'show version' or 'show version detail' to retrieve the installed Junos OS version

Affected if The installed version matches the affected ranges: Junos < 20.4, = 20.4, = 21.2, = 21.3, = 21.4, = 22.1, = 22.2, = 22.3, = 22.4 or Junos OS Evolved < 21.2, = 21.2, = 21.3, = 21.4, = 22.1, = 22.2, = 22.3, = 22.4
Verify rib-sharding configuration

Run 'show configuration | display set | match rib-sharding' or view the routing options configuration to see if rib-sharding is enabled

Affected if rib-sharding is configured and active in the routing daemon configuration
Verify update-threading configuration

Run 'show configuration | display set | match update-threading' or view the BGP group configuration to check if update-threading is enabled

Affected if update-threading is configured under the BGP peer or group configuration
Confirm BGP is configured

Run 'show configuration protocols bgp' to view the BGP configuration and identify configured peers or groups

Affected if BGP is configured with active peers, especially if rib-sharding and update-threading are applied to BGP-specific routing instances

You are affected if your Junos version is in the affected list AND both rib-sharding and update-threading are configured with active BGP peers, enabling the race condition to trigger on BGP peer flapping.

Generated from the published advisory. Verify against your own configuration.

Remediation

dbcve · scoped

Upgrade available Upgrade to 20.4 / 21.2 or later

Fixed in 20.421.2

Interim mitigation

Upgrade Junos OS/Evolved to a patched version listed in the advisory and consider disabling rib-sharding or update-threading as a temporary mitigation if upgrading is not immediately feasible.

Recommended fix High confidence

Upgrade to Junos OS 20.4R3-S8 / 21.2R3-S6 / 21.3R3-S5 / 21.4R3-S4 / 22.1R3-S3 / 22.2R3-S1 / 22.3R3 / 22.4R3 or later, or Junos OS Evolved 21.2R3-S6-EVO / 21.3R3-S5-EVO / 21.4R3-S4-EVO / 22.1R3-S3-EVO / 22.2R3-S1-EVO / 22.3R3-EVO / 22.4R3-EVO or later

1. Identify the current Junos OS or Junos OS Evolved version running on the device using 'show version'
2. Check if BGP rib-sharding and update-threading are configured using 'show configuration protocols bgp' and looking for rib-sharding or update-threading statements
3. If affected version is identified and features are in use, plan for upgrade to fixed version
4. Before upgrade, ensure you have a valid configuration backup and understand the upgrade procedure
5. Upgrade to one of the fixed versions: Junos OS 20.4R3-S8, 21.2R3-S6, 21.3R3-S5, 21.4R3-S4, 22.1R3-S3, 22.2R3-S1, 22.3R3, or 22.4R3 (or later)
5b. For Junos OS Evolved, upgrade to 21.2R3-S6-EVO, 21.3R3-S5-EVO, 21.4R3-S4-EVO, 22.1R3-S3-EVO, 22.2R3-S1-EVO, 22.3R3-EVO, or 22.4R3-EVO (or later)
6. After upgrade, verify rpd is running normally using 'show routing-instance' and 'show bgp summary'
7. Monitor for any BGP peer flaps to confirm the DoS condition is resolved

Caveat Standard Junos upgrade considerations apply - review release notes for compatibility and migration notes

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Junos Scoped from the published advisory

Consultation4.0 h
Implementation8.0 h
Testing4.0 h
Review / QA2.0 h

18.0 hours of engineering $3,200

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Scan for this in your stack

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References

Primary sources

kb.juniper.netVendor Advisory
nvd.nist.govNVD record

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-21597 in production — separate from our analysis above.

Notes0 Guidelines

Know something about CVE-2025-21597?

The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.

The version that genuinely resolved it — not the one the vendor claimed
A config change or rule that shut the vector down
A gotcha in the upgrade path that cost you an afternoon

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here

Verified mitigations, workarounds, and config changes
Version or environment caveats, and links to real fixes
No weaponised exploit code, or anything meant to cause harm
No spam, self-promotion, credentials, or personal data

At a glance

A fix existsUpgrade to 20.4 / 21.2 or later

Severity 5.3 Medium

Exploit likelihood EPSS, next 30 days 0.2%

Affects: Junos

Remediation

Need this fixed?

Fix this in Junos 18 hrs · Moderate

Typical engagement from $3,200

Get a fix See the full breakdown ↓

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You’ll deal with our team directly and deploy the reviewed fix to staging first — never straight to production.

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

Check your environment

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

Scan for this in your stack

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Practitioner notes

No notes yet

Official description

Technical summary

Affected products & versions

CVSS breakdown

Am I affected?

Remediation

References