Related to this other question but in this case the CAF is defined as "An ordered, comma delimited list of allele frequencies...".
I tried using vcffilterjdk and the command suggested by Pierre
java -jar dist/vcffilterjdk.jar -e 'variant.variant.getAttributeAsStringList("CAF","1.0").stream().skip(1L).map(A->Double.parseDouble(A)).anyMatch(A->A<0.01);' input.vcf
but predictably returned an error
java.lang.NumberFormatException: For input string: "0.1]"
##INFO=<ID=CAF,Number=.,Type=String,Description="An ordered, comma delimited list of allele frequencies based on 1000Genomes, starting with the reference allele followed by alternate alleles as ordered in the ALT column. Where a 1000Genomes alternate allele is not in the dbSNPs alternate allele set, the allele is added to the ALT column. The minor allele is the second largest value in the list, and was previuosly reported in VCF as the GMAF. This is the GMAF reported on the RefSNP and EntrezSNP pages and VariationReporter">
chr1 51479 rs116400033 T A . PASS ASP;CAF=[0.8926,0.1074];COMMON=1;G5;G5A;KGPROD;KGPhase1;OTHERKG;RS=116400033;RSPOS=51479;SAO=0;SSR=0;VC=SNV;VLD;VP=0x050000000005170016000100;WGT=1;dbSNPBuildID=132