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Reduce FPs for common JS files #949

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Merged
egibs merged 3 commits into from
May 22, 2025
Merged

Reduce FPs for common JS files #949

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4b26bde
Reduce FPs for common JS files
egibs May 22, 2025
edf3d67
Drop severities
egibs May 22, 2025
aa63695
Merge branch 'main' into tweak-js-rules
egibs May 22, 2025
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16 changes: 8 additions & 8 deletions rules/exec/remote_commands/code_eval.yara
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Original file line number Diff line number Diff line change
Expand Up @@ -50,30 +50,30 @@ rule js_eval_response: critical {
filesize < 1MB and any of ($val*)
}

rule js_eval_near_enough_fromChar: high {
rule js_eval_near_enough_fromChar: medium {
meta:
description = "Likely executes encrypted content"
description = "Evaluates content via String.fromCharCode"
filetypes = "js,ts"

strings:
$exec = /[\s\{]eval\(/
$eval = /[\s\{]eval\(/
$decrypt = "String.fromCharCode"

condition:
filesize < 5MB and all of them and math.abs(@exec - @decrypt) > 384
filesize < 5MB and all of them and math.abs(@eval - @decrypt) > 384
}

rule js_eval_obfuscated_fromChar: critical {
rule js_eval_obfuscated_fromChar: high {
meta:
description = "Likely executes encrypted content"
description = "Likely evaluates encrypted content via fromCharCode"
filetypes = "js,ts"

strings:
$exec = /[\s\{]eval\(/
$eval = /[\s\{]eval\(/
$ref = /fromCharCode\(\w{0,16}\s{0,2}[\-\+\*\^]{0,2}\w{0,16}/

condition:
filesize < 5MB and all of them and math.abs(@exec - @ref) > 384
filesize < 5MB and all of them and math.abs(@eval - @ref) > 384
}

rule js_anonymous_function: medium {
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