I've created a user with a password that contains '%' and ','. When I try to connect,

mongo mongodb://myuser:K+4,%j@mydomain.com:12345/dbname

mongo borks with this error:

2018-07-24T14:18:52.110-0700 E - [main] Assertion failure false src/mongo/util/hex.h 48
2018-07-24T14:18:52.123-0700 I CONTROL [main] 0x558a70c10851 0x558a70c0eeba 0x558a6ff61adc 0x558a709d57b8 0x558a709d6f4b 0x558a709da151 0x558a6ffc3408 0x558a6ffa0e48 0x558a6ff99303 0x558a70bc3011 0x558a70bc3882 0x558a70bc3c0c 0x558a6ff94336 0x558a6ff640fe 0x7f275fee2830 0x558a6ff8e039
----- BEGIN BACKTRACE -----

,{"b":"558A6F8B2000","o":"135CEBA","s":"ZN5mongo10logContextEPKc"},{"b":"558A6F8B2000","o":"6AFADC","s":"_ZN5mongo12verifyFailedEPKcS1_j"},{"b":"558A6F8B2000","o":"11237B8","s":"_ZN5mongo9uriDecodeB5cxx11ENS_10StringDataE"},{"b":"558A6F8B2000","o":"1124F4B","s":"_ZN5mongo8MongoURI9parseImplERKNSt7cxx1112basic_stringIcSt11char_traitsIcESaIcEEE"},{"b":"558A6F8B2000","o":"1128151","s":"_ZN5mongo8MongoURI5parseERKNSt7cxx1112basic_stringIcSt11char_traitsIcESaIcEEE"},{"b":"558A6F8B2000","o":"711408","s":"_ZN5mongo22storeMongoShellOptionsERKNS_17optionenvironment11EnvironmentERKSt6vectorINSt7cxx1112basic_stringIcSt11char_traitsIcESaIcEEESaISA_EE"},{"b":"558A6F8B2000","o":"6EEE48","s":"_ZN5mongo49_mongoInitializerFunction_MongoShellOptions_StoreEPNS_18InitializerContextE"},{"b":"558A6F8B2000","o":"6E7303","s":"_ZNSt17_Function_handlerIFN5mongo6StatusEPNS0_18InitializerContextEEPS4_E9_M_invokeERKSt9_Any_dataOS3"},{"b":"558A6F8B2000","o":"1311011","s":"ZN5mongo11Initializer19executeInitializersERKSt6vectorINSt7cxx1112basic_stringIcSt11char_traitsIcESaIcEEESaIS7_EERKSt3mapIS7_S7_St4lessIS7_ESaISt4pairIKS7_S7_EEE"},{"b":"558A6F8B2000","o":"1311882","s":"_ZN5mongo21runGlobalInitializersEiPKPKcS3"},{"b":"558A6F8B2000","o":"1311C0C","s":"ZN5mongo26runGlobalInitializersOrDieEiPKPKcS3"},{"b":"558A6F8B2000","o":"6E2336","s":"Z5_mainiPPcS0"},{"b":"558A6F8B2000","o":"6B20FE","s":"main"},{"b":"7F275FEC2000","o":"20830","s":"__libc_start_main"},{"b":"558A6F8B2000","o":"6DC039","s":"_start"}]}
mongo(_ZN5mongo15printStackTraceERSo+0x41) [0x558a70c10851]
mongo(_ZN5mongo10logContextEPKc+0x14A) [0x558a70c0eeba]
mongo(_ZN5mongo12verifyFailedEPKcS1_j+0x166) [0x558a6ff61adc]
mongo(_ZN5mongo9uriDecodeB5cxx11ENS_10StringDataE+0x3F8) [0x558a709d57b8]
mongo(ZN5mongo8MongoURI9parseImplERKNSt7_cxx1112basic_stringIcSt11char_traitsIcESaIcEEE+0x80B) [0x558a709d6f4b]
mongo(ZN5mongo8MongoURI5parseERKNSt7_cxx1112basic_stringIcSt11char_traitsIcESaIcEEE+0x31) [0x558a709da151]
mongo(ZN5mongo22storeMongoShellOptionsERKNS_17optionenvironment11EnvironmentERKSt6vectorINSt7_cxx1112basic_stringIcSt11char_traitsIcESaIcEEESaISA_EE+0x1C78) [0x558a6ffc3408]
mongo(_ZN5mongo49_mongoInitializerFunction_MongoShellOptions_StoreEPNS_18InitializerContextE+0x38) [0x558a6ffa0e48]
mongo(ZNSt17_Function_handlerIFN5mongo6StatusEPNS0_18InitializerContextEEPS4_E9_M_invokeERKSt9_Any_dataOS3+0x23) [0x558a6ff99303]
mongo(ZN5mongo11Initializer19executeInitializersERKSt6vectorINSt7_cxx1112basic_stringIcSt11char_traitsIcESaIcEEESaIS7_EERKSt3mapIS7_S7_St4lessIS7_ESaISt4pairIKS7_S7_EEE+0x371) [0x558a70bc3011]
mongo(ZN5mongo21runGlobalInitializersEiPKPKcS3+0x352) [0x558a70bc3882]
mongo(ZN5mongo26runGlobalInitializersOrDieEiPKPKcS3+0x2C) [0x558a70bc3c0c]
mongo(Z5_mainiPPcS0+0xA6) [0x558a6ff94336]
mongo(main+0xE) [0x558a6ff640fe]
libc.so.6(__libc_start_main+0xF0) [0x7f275fee2830]
mongo(_start+0x29) [0x558a6ff8e039]
----- END BACKTRACE -----
UnknownError: assertion src/mongo/util/hex.h:48

For passwords like "K/4,%j", I get "FailedToParse: Bad digit "K" while parsing K".