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CVE-2026-21917 (GCVE-0-2026-21917)

Vulnerability from cvelistv5 – Published: 2026-01-15 20:27 – Updated: 2026-01-15 21:12
VLAI
Title
Junos OS: SRX Series: Specifically malformed SSL packet causes FPC crash
Summary
An Improper Validation of Syntactic Correctness of Input vulnerability in the Web-Filtering module of Juniper Networks Junos OS on SRX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS). If an SRX device configured for UTM Web-Filtering receives a specifically malformed SSL packet, this will cause an FPC crash and restart. This issue affects Junos OS on SRX Series: * 23.2 versions from 23.2R2-S2 before 23.2R2-S5,  * 23.4 versions from 23.4R2-S1 before 23.4R2-S5, * 24.2 versions before 24.2R2-S2, * 24.4 versions before 24.4R1-S3, 24.4R2. Earlier versions of Junos are also affected, but no fix is available.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.7 (High)
CVSS:4.0/AV:N/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
SSVC
Exploitation: none Automatable: yes Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-01-15 21:12 UTC
CWE
  • CWE-1286 - Improper Validation of Syntactic Correctness of Input
Assigner
References
Impacted products
Vendor Product Version CPE status
Juniper Networks Junos OS Affected: 23.2R2-S2 , < 23.2R2-S5 (semver)
Affected: 23.4R2-S1 , < 23.4R2-S5 (semver)
Affected: 24.2 , < 24.2R2-S2 (semver)
Affected: 24.4 , < 24.4R1-S3, 24.4R2 (semver)
guessed Create a notification for this product.
Date Public
2026-01-14 17:00
Show details on NVD website
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    "redhat_vex": {
      "current_release_date": "2026-01-16T21:33:33+00:00",
      "cve": "CVE-2026-21917",
      "id": "CVE-2026-21917",
      "initial_release_date": "2026-01-14T17:00:00+00:00",
      "product_status:known_not_affected": "1",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "Junos OS: SRX Series: Specifically malformed SSL packet causes FPC crash",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-21917.json",
      "version": "3"
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\"en\", \"value\": \"To be exposed to this issue web-filtering needs to be configured as follows:\\n\\n[ security utm utm-policy \u003cutm policy name\u003e web-filtering\\u00a0http-profile \u003cname\u003e ]\\n[\\u00a0security policies ... policy \u003csecurity policy name\u003e then permit application-services utm-policy \u003cutm policy name\u003e ]\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"To be exposed to this issue web-filtering needs to be configured as follows:\u003cbr\u003e\u003cbr\u003e\u003ctt\u003e[ security utm utm-policy \u0026lt;utm policy name\u0026gt; web-filtering\u0026nbsp;http-profile \u0026lt;name\u0026gt; ]\u003cbr\u003e[\u0026nbsp;security policies ... policy \u0026lt;security policy name\u0026gt; then permit application-services utm-policy \u0026lt;utm policy name\u0026gt; ]\u003c/tt\u003e\", \"base64\": false}]}], \"providerMetadata\": {\"orgId\": \"8cbe9d5a-a066-4c94-8978-4b15efeae968\", \"shortName\": \"juniper\", \"dateUpdated\": 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      "dataType": "CVE_RECORD",
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    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.


Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.