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CozyDuke / CozyCar / CozyBear Implant by APT29

yara CRITICAL Yara-Rules
aptcommunity
This rule was pulled from an open-source repository and enriched with AI. Validate in a test environment before deploying to production.
View original rule at Yara-Rules →
Retrieved: 2026-05-26T11:00:01Z · Confidence: medium

Hunt Hypothesis

The detection identifies potential CozyDuke / CozyCar / CozyBear implants deployed by APT29, leveraging unusual network traffic patterns indicative of C2 communication. SOC teams should proactively hunt for this behavior to detect and mitigate advanced persistent threats before they exfiltrate sensitive data or escalate within the environment.

YARA Rule

rule IMPLANT_10_v2 {
   meta:
      description = "CozyDuke / CozyCar / CozyBear Implant by APT29"
      author = "US CERT"
      reference = "https://www.us-cert.gov/ncas/current-activity/2017/02/10/Enhanced-Analysis-GRIZZLY-STEPPE"
      date = "2017-02-10"
      score = 85
   strings:
      $xor = { 34 ?? 66 33 C1 48 FF C1 }
      $nop = { 66 66 66 66 66 66 0f 1f 84 00 00 00 00 00}
   condition:
      uint16(0) == 0x5A4D and $xor and $nop
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

This rule contains 2 string patterns in its detection logic.

References

False Positive Guidance

Original source: https://github.com/Yara-Rules/rules/blob/main/malware/APT_Grizzlybear_uscert.yar