CVE-2025-52951
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.
NVD · uneditedA Protection Mechanism Failure vulnerability in kernel filter processing of Juniper Networks Junos OS allows an attacker sending IPv6 traffic destined to the device to effectively bypass any firewall filtering configured on the interface. Due to an issue with Junos OS kernel filter processing, the 'payload-protocol' match is not being supported, causing any term containing it to accept all packets without taking any other action. In essence, these firewall filter terms were being processed as an 'accept' for all traffic on the interface destined for the control plane, even when used in combination with other match criteria. This issue only affects firewall filters protecting the device's control plane. Transit firewall filtering is unaffected by this vulnerability. This issue affects Junos OS: * all versions before 21.2R3-S9, * from 21.4 before 21.4R3-S11, * from 22.2 before 22.2R3-S7, * from 22.4 before 22.4R3-S7, * from 23.2 before 23.2R2-S4, * from 23.4 before 23.4R2-S5, * from 24.2 before 24.2R2-S1, * from 24.4 before 24.4R1-S2, 24.4R2. This is a more complete fix for previously published CVE-2024-21607 (JSA75748).
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.
dbcve analysis · high confidenceA Protection Mechanism Failure in Junos OS kernel filter processing causes the 'payload-protocol' match criterion to fail, causing any firewall filter term containing it to accept all IPv6 packets regardless of other match criteria. This allows bypass of control-plane firewall filters for IPv6 traffic destined to the device.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
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.
NVD · CPE data< 21.2= 21.2= 21.4= 22.2= 22.4= 23.2= 23.4= 24.2= 24.4CVSS 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.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
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.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check Junos OS versionRun 'show version' or 'show version detail' to display the installed Junos OS versionAffected if The installed version is < 21.2, or exactly 21.2, 21.4, 22.2, 22.4, 23.2, 23.4, 24.2, or 24.4
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Identify firewall filters with payload-protocol matchRun 'show configuration firewall' or 'show configuration | match payload-protocol' to search for any filter terms using the 'payload-protocol' match criterionAffected if Any firewall filter term contains the 'payload-protocol' match criterion, regardless of other conditions
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Verify IPv6 input filters applied to the deviceRun 'show configuration interfaces lo0 unit 0 family inet6' or 'show configuration protocols mgd-agent' to check for control-plane IPv6 filters; also run 'show firewall' to list active firewall filtersAffected if An IPv6 input filter is applied to the loopback or management interface and it uses payload-protocol matching
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Confirm payload-protocol is used in input filtersRun 'show configuration firewall filter <filter-name>' for each filter identified, examining the 'from payload-protocol' terms under 'then' or 'from' blocksAffected if The filter is applied as an input filter and contains 'payload-protocol' match criteria
You are affected if your Junos OS version matches one of the listed affected versions AND you have any firewall filter containing the 'payload-protocol' match criterion applied to IPv6 traffic.
Generated from the published advisory. Verify against your own configuration.
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.
dbcve · scoped21.2
Apply the vendor-supplied Junos OS patches for the specific version branches (21.2R3-S9, 21.4R3-S11, 22.2R3-S7, 22.4R3-S7, 23.2R2-S4, 23.4R2-S5, 24.2R2-S1, 24.4R1-S2 or later). Review existing control-plane firewall filters to identify and validate any terms using 'payload-protocol' match until patches can be applied.
Upgrade to the appropriate S-series maintenance release for your current branch (21.2R3-S9+, 21.4R3-S11+, 22.2R3-S7+, 22.4R3-S7+, 23.2R2-S4+, 23.4R2-S5+, 24.2R2-S1+, or 24.4R1-S2+/24.4R2+)
- 1. Identify the current Junos OS version running on the device using 'show version'
- 2. Determine the currently deployed Junos branch (21.2, 21.4, 22.2, 22.4, 23.2, 23.4, 24.2, or 24.4)
- 3. Plan maintenance window for upgrade as control plane filtering will be temporarily affected
- 4. Download the appropriate fixed release for your branch: for 21.2.x upgrade to 21.2R3-S9 or later; for 21.4.x upgrade to 21.4R3-S11 or later; for 22.2.x upgrade to 22.2R3-S7 or later; for 22.4.x upgrade to 22.4R3-S7 or later; for 23.2.x upgrade to 23.2R2-S4 or later; for 23.4.x upgrade to 23.4R2-S5 or later; for 24.2.x upgrade to 24.2R2-S1 or later; for 24.4.x upgrade to 24.4R1-S2 or later, or 2
- 5. Upload the new Junos image to the device using 'file copy' or USB
- 6. Initiate the upgrade using 'request system software add <package> reboot'
- 7. After reboot, verify the new version is running with 'show version'
- 8. Confirm the fix by reviewing 'show configuration | display json | match payload-protocol' to ensure proper filter configuration
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA4.0 h
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2025-52951 in production — separate from our analysis above.
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
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