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JunosOperating system · Juniper

CVE-2023-36841

HIGH · 7.5 CVSS v3.1 Published 2023-10-12
Fix available
A fix is available. Upgrade to 20.4 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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 · unedited
An Improper Check for Unusual or Exceptional Conditions vulnerability in the Packet Forwarding Engine (pfe) of Juniper Networks Junos OS on MX Series allows a unauthenticated network-based attacker to cause an infinite loop, resulting in a Denial of Service (DoS). An attacker who sends malformed TCP traffic via an interface configured with PPPoE, causes an infinite loop on the respective PFE. This results in consuming all resources and a manual restart is needed to recover. This issue affects interfaces with PPPoE configured and tcp-mss enabled. This issue affects Juniper Networks Junos OS * All versions prior to 20.4R3-S7; * 21.1 version 21.1R1 and later versions; * 21.2 versions prior to 21.2R3-S6; * 21.3 versions prior to 21.3R3-S5; * 21.4 versions prior to 21.4R3-S3; * 22.1 versions prior to 22.1R3-S4; * 22.2 versions prior to 22.2R3; * 22.3 versions prior to 22.3R2-S2; * 22.4 versions prior to 22.4R2;

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 confidence

A vulnerability in the Packet Forwarding Engine (PFE) of Juniper Networks Junos OS on MX Series allows an unauthenticated network attacker to cause an infinite loop by sending malformed TCP traffic through interfaces configured with PPPoE and tcp-mss enabled. This consumes all PFE resources and requires a manual device restart to recover.

MitigationUpgrade Junos OS to a fixed version (21.1R1+, 21.2R3-S6+, 21.3R3-S5+, 21.4R3-S3+, 22.1R3-S4+, 22.2R3+, 22.3R2-S2+, or 22.4R2+) as listed in the vendor advisory; no explicit workarounds are mentioned in the description.

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
JunosOperating system
Affected:< 20.4= 20.4= 21.1= 21.2= 21.3= 21.4= 22.1= 22.2= 22.3= 22.4

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.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

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 checks

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

  1. Identify Junos OS version
    Run 'show version' or 'show version detail' to obtain the installed Junos OS version
    Affected if The version matches any of these: < 20.4, 20.4, 21.1, 21.2, 21.3, 21.4, 22.1, 22.2, 22.3, 22.4 (compare your installed version to these affected ranges)
  2. Confirm device is MX Series
    Run 'show chassis hardware' or 'show version' to identify the hardware model; MX Series platforms include MX5, MX10, MX40, MX80, MX104, MX240, MX480, MX960, and virtual MX (vMX)
    Affected if The device is an MX Series router
  3. Check for PPPoE interface configuration
    Run 'show configuration interfaces | display set | match pppoe' to search for PPPoE-related interface configuration in the active config
    Affected if Any interfaces are configured with PPPoE (protocol pppoe)
  4. Verify tcp-mss is enabled on PPPoE interfaces
    Run 'show configuration interfaces <interface-name> unit <unit> family inet filter input <filter-name>' and look for 'tcp-mss' in any firewall filter applied to PPPoE interfaces; alternatively, search the config with 'show configuration | match tcp-mss'
    Affected if tcp-mss is configured in a firewall filter applied to PPPoE interfaces
  5. Check for PFE resource exhaustion symptoms
    Run 'show chassis fpc' and 'show pfe statistics traffic' to monitor PFE CPU and memory utilization; look for sustained high utilization or increasing error counters
    Affected if PFE resources are fully consumed or showing abnormal traffic patterns indicative of an infinite loop

You are affected if your MX Series device runs a vulnerable Junos version (20.4 through 22.4) AND has PPPoE interfaces with tcp-mss enabled, and you observe PFE resource exhaustion from malformed TCP traffic.

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

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to 20.4 or later
Fixed in 20.4
Interim mitigation

Upgrade Junos OS to a fixed version (21.1R1+, 21.2R3-S6+, 21.3R3-S5+, 21.4R3-S3+, 22.1R3-S4+, 22.2R3+, 22.3R2-S2+, or 22.4R2+) as listed in the vendor advisory; no explicit workarounds are mentioned in the description.

Recommended fix High confidence

20.4R3-S7, 21.2R3-S6, 21.3R3-S5, 21.4R3-S3, 22.1R3-S4, 22.2R3, 22.3R2-S2, or 22.4R2 (depending on desired maintenance branch)

  1. 1. Identify the current Junos OS version running on the MX Series device using 'show version'
  2. 2. Identify the maintenance branch currently in use (e.g., 20.4, 21.1, 21.2, 21.3, 21.4, 22.1, 22.2, 22.3, or 22.4)
  3. 3. Upgrade to the minimum fixed version for that branch: 20.4R3-S7, 21.2R3-S6, 21.3R3-S5, 21.4R3-S3, 22.1R3-S4, 22.2R3, 22.3R2-S2, or 22.4R2
  4. 4. After upgrade, verify the device is operational and the PPPoE interfaces are functioning correctly
  5. 5. Consider upgrading to the most recent stable release within the branch for additional fixes
Caveat Standard Junos OS upgrade precautions apply - review release notes for known issues and ensure compatibility with existing configurations

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

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-36841 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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