CVE-2026-21921 (GCVE-0-2026-21921)

Vulnerability from cvelistv5 – Published: 2026-01-15 20:28 – Updated: 2026-01-15 20:55
VLAI
Title
Junos OS and Junos OS Evolved: When telemetry collectors are frequently subscribing and unsubscribing to sensors chassisd or rpd will crash
Summary
A Use After Free vulnerability in the chassis daemon (chassisd) of Juniper Networks Junos OS and Junos OS Evolved allows a network-based attacker authenticated with low privileges to cause a Denial-of-Service (DoS). When telemetry collectors are frequently subscribing and unsubscribing to sensors continuously over a long period of time, telemetry-capable processes like chassisd, rpd or mib2d will crash and restart, which - depending on the process - can cause a complete outage until the system has recovered. This issue affects:  Junos OS:  * all versions before 22.4R3-S8, * 23.2 versions before 23.2R2-S5, * 23.4 versions before 23.4R2; Junos OS Evolved: * all versions before 22.4R3-S8-EVO, * 23.2 versions before 23.2R2-S5-EVO, * 23.4 versions before 23.4R2-EVO.
Severity
6.5 (Medium)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
7.1 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:A/RE:M
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-01-15 20:54 UTC
CWE
Assigner
References
Impacted products
Vendor Product Version CPE status
Juniper Networks Junos OS Affected: 0 , < 22.4R3-S8 (semver)
Affected: 23.2 , < 23.2R2-S5 (semver)
Affected: 23.4 , < 23.4R2 (semver)
guessed Create a notification for this product.
Juniper Networks Junos OS Evolved Affected: 0 , < 22.4R3-S8-EVO (semver)
Affected: 23.2 , < 23.2R2-S5-EVO (semver)
Affected: 23.4 , < 23.4R2-EVO (semver)
guessed Create a notification for this product.
Date Public
2026-01-14 17:00
Show details on NVD website
To clipboard 

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              "value": "The following software releases have been updated to resolve this specific issue:\nJunos OS Evolved: 22.4R3-S8-EVO, 23.2R2-S5-EVO, 23.4R2-EVO, 24.2R1-EVO,\u00a0and all subsequent releases;\nJunos OS: 22.4R3-S8, 23.2R2-S5, 23.4R2, 24.2R1, and all subsequent releases."
            }
          ],
          "source": {
            "advisory": "JSA106021",
            "defect": [
              "1791928"
            ],
            "discovery": "INTERNAL"
          },
          "title": "Junos OS and Junos OS Evolved: When telemetry collectors are frequently subscribing and unsubscribing to sensors chassisd or rpd will crash",
          "workarounds": [
            {
              "lang": "en",
              "supportingMedia": [
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                  "type": "text/html",
                  "value": "There are no known workarounds for this issue."
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              "value": "There are no known workarounds for this issue."
            }
          ],
          "x_generator": {
            "engine": "Vulnogram 0.1.0-dev"
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      "cveMetadata": {
        "assignerOrgId": "8cbe9d5a-a066-4c94-8978-4b15efeae968",
        "assignerShortName": "juniper",
        "cveId": "CVE-2026-21921",
        "datePublished": "2026-01-15T20:28:29.656Z",
        "dateReserved": "2026-01-05T17:32:48.712Z",
        "dateUpdated": "2026-01-15T20:55:25.182Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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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.



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.