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CVE-2021-31364

Junos OS: SRX Series: The flowd process will crash if log session-close is configured and specific traffic is received

Medium5.9EPSS 0.66%
Published
Updated
Reserved
Assigned by
juniper

Description

An Improper Check for Unusual or Exceptional Conditions vulnerability combined with a Race Condition in the flow daemon (flowd) of Juniper Networks Junos OS on SRX300 Series, SRX500 Series, SRX1500, and SRX5000 Series with SPC2 allows an unauthenticated network based attacker sending specific traffic to cause a crash of the flowd/srxpfe process, responsible for traffic forwarding in SRX, which will cause a Denial of Service (DoS). Continued receipt and processing of this specific traffic will create a sustained Denial of Service (DoS) condition. This issue can only occur when specific packets are trying to create the same session and logging for session-close is configured as a policy action. Affected platforms are: SRX300 Series, SRX500 Series, SRX1500, and SRX5000 Series with SPC2. Not affected platforms are: SRX4000 Series, SRX5000 Series with SPC3, and vSRX Series. This issue affects Juniper Networks Junos OS SRX300 Series, SRX500 Series, SRX1500, and SRX5000 Series with SPC2: All versions prior to 17.4R3-S5; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R3-S9; 19.1 versions prior to 19.1R3-S6; 19.2 versions prior to 19.2R1-S7, 19.2R3-S2; 19.3 versions prior to 19.3R2-S6, 19.3R3-S2; 19.4 versions prior to 19.4R1-S4, 19.4R3-S3; 20.1 versions prior to 20.1R2-S2, 20.1R3; 20.2 versions prior to 20.2R3; 20.3 versions prior to 20.3R2-S1, 20.3R3; 20.4 versions prior to 20.4R2.

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-2021-31364, by who scored it
Scored byCVSSScoreVector
juniperCNA (assigner)3.1Medium5.9CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
NVDNVD · Modified3.1Medium5.9CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS (exploitation in 30 days)
0.66% · top 48% 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 5.9.

Weakness

Affected products

  • Juniper Networks · Junos OS

    • affected unspecified – < 17.4R3-S5
    • affected 18.3 – < 18.3R3-S5
    • affected 18.4 – < 18.4R3-S9
    • affected 19.1 – < 19.1R3-S6
    • affected 19.2 – < 19.2R1-S7, 19.2R3-S2
    • affected 19.3 – < 19.3R2-S6, 19.3R3-S2
    • affected 19.4 – < 19.4R1-S4, 19.4R3-S3
    • affected 20.1 – < 20.1R2-S2, 20.1R3
    • affected 20.2 – < 20.2R3
    • affected 20.3 – < 20.3R2-S1, 20.3R3
    • affected 20.4 – < 20.4R2

What to do

Solution: The following software releases have been updated to resolve this specific issue: 17.4R3-S5, 18.3R3-S5, 18.4R3-S9, 19.1R3-S6, 19.2R1-S7, 19.2R3-S2, 19.3R2-S6, 19.3R3-S2, 19.4R1-S4, 19.4R3-S3, 20.1R2-S2, 20.1R3, 20.2R3, 20.3R2-S1, 20.3R3, 20.4R2, 21.1R1, and all subsequent releases.

Workaround: Please remove the session-close log action from the policy actions of all policies.

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 .