BRUSHFIRE is a passive backdoor written in C that executes in-memory within an existing process. First reported in March 2025, BRUSHFIRE has been observed in activity attributed to People's Republic of China (PRC) state-affiliated threat actors, including UNC5221 and SYLVANITE.[1][2][3]
4
TechniquesBottom 17%
4
Tactics32nd pct
0
Threat groupsNone recorded
0
CampaignsNone recorded
Enterprise ATT&CK only. Any Mobile or ICS rows on the same ATT&CK page are not carried.
BRUSHFIRE has the ability to exfiltrate data on-demand through executing commands obtained via monitoring for specially crafted packets and sending output back in an embedded SSL response.4
BRUSHFIRE has monitored inbound VPN traffic to compromised appliances until specific inbound packets contain a specific magic string/pattern instead of external beaconing.6
Persistence · Stealth · Command and Controlno detection rules
BRUSHFIRE has executed its commands within memory and is not saved on disk.78
Stealth5 detection rules
Standing S9011
Reach is how much of ATT&CK this malware touches. Coverage is how well defended each thing it does is, as a median per technique rather than a total — a total would just restate the reach. Each figure is ranked against all 825 ATT&CK software entries only where that population actually spreads. Where most of the population shares one value, a percentile would rank the tie instead of the entity, so the raw value is shown and no rank is claimed.
Reach
Techniques4Bottom 17%
17th percentile · 83% of 825 ATT&CK software entries have more Enterprise techniques.
Tactics432nd pct
32nd percentile · 68% of 825 ATT&CK software entries have more tactics spanned.
Threat groups061% tie · 22 values
61% of the population shares a single value across only 22 distinct values, so a percentile here would rank the tie, not the entity.
Campaigns085% tie · 8 values
85% of the population shares a single value across only 8 distinct values, so a percentile here would rank the tie, not the entity.
Coverage
Rules / technique2.5medBottom 2%
2nd percentile · 98% of 825 ATT&CK software entries have more detection rules per technique.
Tests / technique3.5medBottom 19%
19th percentile · 81% of 825 ATT&CK software entries have more atomic tests per technique.
Data comps / technique5med54% tie · 11 values
54% of the population shares a single value across only 11 distinct values, so a percentile here would rank the tie, not the entity.
Mitigations / technique1med57th pct
57th percentile · 57% of 825 ATT&CK software entries have this many mitigations per technique or fewer.
5 of 8 axes carry an honest rank on this page. Coverage medians are taken across this malware’s 4 Enterprise techniques.
Range
Technique Campaign use over its cumulative rule count.
The following analytic detects the use of CertUtil.exe with the 'decode' argument, which may indicate an attempt to decode a previously encoded file, potentially containing malicious payloads. (...)
The following analytic detects suspicious Base64 decode operations that may indicate malicious activity, such as data exfiltration or execution of encoded commands. (...)
Detects the use of tail to extract bytes at an offset from an image and then decode the base64 value to create a new file with the decoded content. (...)
The following analytic detects PowerShell Script Block Logging (Event ID 4104) evidence of a complete P/Invoke process-injection API chain at either the compile phase or the execution phase. (...)
The following analytic identifies when a Windows process loads scripting libraries like jscript.dll or vbscript.dll to execute script code on a target system. (...)