CVE-2026-33774Network attack vector

Firewall bypass via skipped loopback input filters

Published Apr 9, 2026 · Updated Apr 9, 2026

Improper condition checking in the Junos OS PFE on Juniper Networks MX Series allows remote attackers to bypass filters and reach the control plane. The PFE skips an input filter on lo0.n when n is nonzero and the interface belongs to the global VRF because no routing-instance references it. Exposure requires an MX304 or an MX chassis with MPC10, MPC11, LC4800, or LC9600 hardware and this loopback configuration; matching control-plane traffic is accepted without the intended filter.

CVSS severity6.5
Medium
EPSS probability0.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper condition checking in the Junos OS PFE on Juniper Networks MX Series allows remote attackers to bypass filters and reach the control plane. The PFE skips an input filter on lo0.n when n is nonzero and the interface belongs to the global VRF because no routing-instance references it. Exposure requires an MX304 or an MX chassis with MPC10, MPC11, LC4800, or LC9600 hardware and this loopback configuration; matching control-plane traffic is accepted without the intended filter.

The record

CVE
CVE-2026-33774
Published
Apr 9, 2026
Updated
Apr 9, 2026
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-754, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=0 <23.2R2-S6
  2. Affected versionversion=23.4 <23.4R2-S7
  3. Affected versionversion=24.2 <24.2R2
  4. Affected versionversion=24.4 <24.4R2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=0 <23.2R2-S6; version=23.4 <23.4R2-S7; version=24.2 <24.2R2; version=24.4 <24.4R2

Published CVSS scores

6.5Juniper NetworksCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
6.9Juniper NetworksCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-754Improper Check for Unusual or Exceptional Conditions
T1190Exploit Public-Facing Application

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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