CVE-2021-21404 (GCVE-0-2021-21404)

Vulnerability from cvelistv5 – Published: 2021-04-06 20:00 – Updated: 2024-08-03 18:09
VLAI
Title
Crash due to malformed relay protocol message
Summary
Syncthing is a continuous file synchronization program. In Syncthing before version 1.15.0, the relay server `strelaysrv` can be caused to crash and exit by sending a relay message with a negative length field. Similarly, Syncthing itself can crash for the same reason if given a malformed message from a malicious relay server when attempting to join the relay. Relay joins are essentially random (from a subset of low latency relays) and Syncthing will by default restart when crashing, at which point it's likely to pick another non-malicious relay. This flaw is fixed in version 1.15.0.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE
  • CWE-20 - Improper Input Validation
Assigner
References
Impacted products
Vendor Product Version CPE status
syncthing syncthing Affected: < 1.15.0
guessed Create a notification for this product.
Show details on NVD website
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      "current_release_date": "2025-11-21T16:18:31+00:00",
      "cve": "CVE-2021-21404",
      "id": "CVE-2021-21404",
      "initial_release_date": "2021-04-07T00:00:00+00:00",
      "product_status:known_not_affected": "1",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "syncthing: sending a relay message with a negative length field may lead to crash",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2021/cve-2021-21404.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2025-03-15T09:10:49Z",
      "cve": "CVE-2021-21404",
      "id": "CVE-2021-21404",
      "initial_release_date": "2023-02-15T03:46:15Z",
      "product_status:recommended": "6",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2021-21404",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2021-21404.json",
      "version": "7"
    }
  }
}



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Tags
Taxonomy of the tags.





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.