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JunosOperating system · Juniper

CVE-2021-0249

CRITICAL · 9.8 CVSS v3.1 Published 2021-04-22
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
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
On SRX Series devices configured with UTM services a buffer overflow vulnerability in the Packet Forwarding Engine (PFE) of Juniper Networks Junos OS may allow an attacker to arbitrarily execute code or commands on the target to take over or otherwise impact the device by sending crafted packets to or through the device. This issue affects: Juniper Networks Junos OS on SRX Series: 15.1X49 versions prior to 15.1X49-D190; 17.4 versions prior to 17.4R2-S9; 17.4R3 and later versions prior to 18.1R3-S9; 18.2 versions prior to 18.2R3-S1; 18.3 versions prior to 18.3R2-S3, 18.3R3; 18.4 versions prior to 18.4R2-S3, 18.4R3; 19.1 versions prior to 19.1R1-S4, 19.1R2; 19.2 versions prior to 19.2R1-S1, 19.2R2. An indicator of compromise can be the following text in the UTM log: RT_UTM: AV_FILE_NOT_SCANNED_PASSED_MT:

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 buffer overflow vulnerability exists in the Packet Forwarding Engine (PFE) of Juniper Networks Junos OS on SRX Series devices with UTM services enabled. Remote attackers can achieve arbitrary code execution by sending crafted packets to or through the affected device. This critical flaw (CVSS 9.8) affects multiple version branches of Junos OS.

MitigationUpgrade Junos OS to the patched versions specified (15.1X49-D190, 17.4R2-S9, 18.1R3-S9, 18.2R3-S1, 18.3R2-S3/18.3R3, 18.4R2-S3/18.4R3, 19.1R1-S4/19.1R2, 19.2R1-S1/19.2R2). Review UTM logs for indicator 'RT_UTM: AV_FILE_NOT_SCANNED_PASSED_MT:' as a potential compromise indicator.

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:= 15.1x49= 17.4= 18.1= 18.2= 18.3= 18.4= 19.1= 19.2

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
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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 device model
    Run 'show chassis hardware' or 'show system information' to confirm the device is an SRX Series firewall
    Affected if Device is not an SRX Series device - this vulnerability only affects SRX Series
  2. Verify Junos OS version
    Run 'show version' to obtain the installed Junos OS version
    Affected if Version matches 15.1x49, 17.4, 18.1, 18.2, 18.3, 18.4, 19.1, or 19.2 (any variant within these branches)
  3. Confirm UTM is enabled
    Run 'show utm status' or check the configuration with 'show configuration | display set | match utm'
    Affected if UTM (Unified Threat Management) services are actively enabled on the device - the vulnerability requires UTM to be running
  4. Inspect UTM logs for compromise indicators
    Run 'show log messages | match RT_UTM' or review UTM audit logs for the string 'RT_UTM: AV_FILE_NOT_SCANNED_PASSED_MT:'
    Affected if This specific log signature is present, indicating potential exploitation activity

Device is affected if it is an SRX Series firewall running a vulnerable Junos version (15.1x49 through 19.2) with UTM services enabled.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Junos OS to the patched versions specified (15.1X49-D190, 17.4R2-S9, 18.1R3-S9, 18.2R3-S1, 18.3R2-S3/18.3R3, 18.4R2-S3/18.4R3, 19.1R1-S4/19.1R2, 19.2R1-S1/19.2R2). Review UTM logs for indicator 'RT_UTM: AV_FILE_NOT_SCANNED_PASSED_MT:' as a potential compromise indicator.

Recommended fix High confidence

Upgrade to a fixed Junos OS release (e.g., 15.1X49-D190, 17.4R2‑S9, 18.1R3‑S9, 18.2R3‑S1, 18.3R2‑S3, 18.4R2‑S3, 19.1R1‑S4, or 19.2R1‑S1) or later.

  1. Run 'show version' to determine the currently installed Junos OS version.
  2. Verify if the device is configured with UTM (e.g., 'show configuration | display set | match utm').
  3. Review the list of vulnerable versions and confirm that the current version is affected.
  4. Plan the upgrade: identify the appropriate fixed release from Juniper's documentation (e.g., 15.1X49-D190, 17.4R2‑S9, 18.1R3‑S9, 18.2R3‑S1, 18.3R2‑S3, 18.4R2‑S3, 19.1R1‑S4, 19.2R1‑S1).
  5. Back up the current configuration and system image (e.g., 'save /var/tmp/config.boot').
  6. Download the Junos OS software package for the selected fixed release from the Juniper Networks support portal.
  7. Transfer the package to the SRX device (e.g., using SCP or FTP to /var/tmp/).
  8. Install the software using 'request system software add <path> no-copy' (e.g., 'request system software add /var/tmp/junos‑os‑18.2R3‑S1‑signed.tgz no-copy').
Caveat Upgrading Junos OS will cause a reboot and temporary service interruption; review release notes for any configuration or feature changes.

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-2021-0249 in production — separate from our analysis above.

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