CVE-2021-31364Network attack vector

Traffic-forwarding crash via same-session packet race

Published Oct 19, 2021 · Updated Sep 17, 2024

Denial of service in Juniper Networks Junos OS on affected SRX devices allows remote attackers to crash forwarding via specific packets. The flowd daemon races while processing packets that create the same session and improperly handles the exceptional condition, crashing flowd or srxpfe. The flaw requires session-close logging as a policy action; continued traffic sustains the forwarding outage.

CVSS severity5.9
Medium
EPSS probability0.66%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Juniper Networks Junos OS on affected SRX devices allows remote attackers to crash forwarding via specific packets. The flowd daemon races while processing packets that create the same session and improperly handles the exceptional condition, crashing flowd or srxpfe. The flaw requires session-close logging as a policy action; continued traffic sustains the forwarding outage.

The record

CVE
CVE-2021-31364
Published
Oct 19, 2021
Updated
Sep 17, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-754, CWE-362, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 19, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=18.3 <18.3R3-S5
  2. Affected versionversion=18.4 <18.4R3-S9
  3. Affected versionversion=19.1 <19.1R3-S6
  4. Affected versionversion=19.2 <19.2R1-S7, 19.2R3-S2
  5. Affected versionversion=19.3 <19.3R2-S6, 19.3R3-S2
  6. Affected versionversion=19.4 <19.4R1-S4, 19.4R3-S3
  7. Affected versionversion=20.1 <20.1R2-S2, 20.1R3
  8. Affected versionversion=20.2 <20.2R3
  9. Affected versionversion=20.3 <20.3R2-S1, 20.3R3
  10. Affected versionversion=20.4 <20.4R2
  11. Affected versionversion=unspecified <17.4R3-S5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=18.3 <18.3R3-S5; version=18.4 <18.4R3-S9; version=19.1 <19.1R3-S6; version=19.2 <19.2R1-S7, 19.2R3-S2; version=19.3 <19.3R2-S6, 19.3R3-S2; version=19.4 <19.4R1-S4, 19.4R3-S3; version=20.1 <20.1R2-S2, 20.1R3; version=20.2 <20.2R3; version=20.3 <20.3R2-S1, 20.3R3; version=20.4 <20.4R2; version=unspecified <17.4R3-S5

Published CVSS scores

5.9Juniper NetworksCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
4.3NVDAV:N/AC:M/Au:N/C:N/I:N/A:P

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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
CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
T1499.004Application or System Exploitation

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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