2026-07 Security Bulletin: Junos OS: MX Series: Specific traffic causes an FPC to reset (CVE-2026-57019)

Product Affected

This issue affects all versions of Junos OS. Affected platforms: MX Series.

Severity

Medium

Severity Assessment (CVSS) Score

CVSS: v3.1: 6.5 (CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
CVSS: v4.0: 7.1 (CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:A/RE:M)

Problem

An Improper Validation of Specified Quantity in Input vulnerability in the Packet Forwarding Engine (pfe) of Juniper Networks Junos OS on MX Series allows an unauthenticated, adjacent attacker to cause a Denial-of-Service (DoS).

When a specific packet is received from device in the same broadcast domain, an affected system calculates the packet size incorrectly. This causes further packet processing to fail, which triggers an FPC major error, resulting in a FPC reset impacting traffic until the FPC has automatically recovered.

Affected scenarios are: MAP-T, or non-IP traffic encapsulated in IP (e.g. MPLS over GRE).

When this issue happens the following logs can be observed:

fpc<#> CMError: /fpc/0/pfe/0/cm/0/MQSS(0)/0/MQSS_CMERROR_LI_INT_REG_UNROLL_TAIL_LENGTH_OVF (0x2205eb), scope: pfe, category: functional, severity: major, module: MQSS(0), type: LI: Unroll TAIL length overflow, oc_category: defaultfpc<#> Performing action reset-fru for error /fpc/0/pfe/0/cm/0/MQSS(0)/0/MQSS_CMERROR_LI_INT_REG_UNROLL_TAIL_LENGTH_OVF (0x2205eb) in module: MQSS(0) with scope: pfe category: functional level: major, oc_category: default

This issue affects Junos OS on MX Series:

all versions before 23.2R2-S6,
23.4 versions before 23.4R2-S7,
24.2 versions before 24.2R2-S4,
24.4 versions before 24.4R2-S4,
25.2 versions before 25.2R2.

Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

This issue was seen during production usage.

This issue has been assigned CVE-2026-57019.

Solution

The following software releases have been updated to resolve this specific issue: Junos OS: 23.2R2-S6, 23.4R2-S7, 24.2R2-S4, 24.4R2-S4, 25.2R2, 25.4R1, and all subsequent releases.

This issue is being tracked as 1912053 which is visible on the Customer Support website.

Note: Juniper SIRT's policy is not to evaluate releases which are beyond End of Engineering (EOE) or End of Life (EOL).

Workaround

There are no known workarounds for this issue.

Severity Assessment

Information for how Juniper Networks uses CVSS can be found at KB 16446 [juniper.net] "Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories."

Modification History