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CVE-2021-0256

Junos OS: mosquitto Local Privilege Escalation vulnerability in SUID binaries

Medium5.5EPSS 0.21%
Published
Updated
Reserved
Assigned by
juniper

Description

A sensitive information disclosure vulnerability in the mosquitto message broker of Juniper Networks Junos OS may allow a locally authenticated user with shell access the ability to read portions of sensitive files, such as the master.passwd file. Since mosquitto is shipped with setuid permissions enabled and is owned by the root user, this vulnerability may allow a local privileged user the ability to run mosquitto with root privileges and access sensitive information stored on the local filesystem. This issue affects Juniper Networks Junos OS: 17.3 versions prior to 17.3R3-S12, 17.4 versions prior to 17.4R3-S4; 18.1 versions prior to 18.1R3-S12; 18.3 versions prior to 18.3R3-S4; 19.1 versions prior to 19.1R3-S4; 19.3 versions prior to 19.3R3-S1, 19.3R3-S2; 19.4 versions prior to 19.4R2-S3; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R1-S3, 20.2R2, 20.2R3.

Timeline

  1. ID reserved

    By juniper

  2. · 6 months later

    Published

  3. · 3 years later

    Record updated

Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.

Scores

CVSS scores of CVE-2021-0256, by who scored it
Scored byCVSSScoreVector
juniperCNA (assigner)3.1Medium5.5CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
NVDNVD · Modified3.1Medium5.5CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
EPSS (exploitation in 30 days)
0.21% · top 89% of all CVEs (7 Nov 2026)
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.5.

Weakness

Affected products

  • Juniper Networks · Junos OS

    • affected 17.3 – < 17.3R3-S12
    • affected 17.4 – < 17.4R3-S4
    • affected 18.1 – < 18.1R3-S12
    • affected 18.3 – < 18.3R3-S4
    • affected 19.1 – < 19.1R3-S4
    • affected 19.3 – < 19.3R3-S1, 19.3R3-S2
    • affected 19.4 – < 19.4R2-S3
    • affected 20.1 – < 20.1R2
    • affected 20.2 – < 20.2R1-S3, 20.2R2, 20.2R3

What to do

Solution: The following software releases have been updated to resolve this specific issue: Junos OS 17.3R3-S12, 17.4R3-S4, 18.1R3-S12, 19.1R3-S4, 19.3R3-S1, 19.3R3-S2, 19.4R2-S3, 20.1R2, 20.2R1-S3, 20.2R2, 20.2R3, 20.3R1, and all subsequent releases.

Workaround: Use access lists or firewall filters to limit access to the device only from trusted hosts. Limit shell access to only trusted system administrators.

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

References (1)

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .