[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxCezFYO5wG-1-SC2GUJgnZ5QAmrqjsdsPQtcYZkChIc":3},{"id":4,"question":5,"answer":6,"answerHtml":7,"slug":8,"keywords":9,"article":10,"status":34,"aiModel":39,"aiConfidence":39,"updatedAt":51,"createdAt":51,"_status":50},945,"What are the two general methods for decrypting Zyxel firmware discussed in the article?","The article introduces two methods: first, decrypting ZIP files via a known-plaintext attack using tools like pkcrack; second, obtaining the ZIP encryption password by tracking process parameters with `strace` on a MIPS-emulated environment where `zld_fsextract` runs. Both methods are detailed in the [Zyxel Firmware Decryption](\u002Fnews\u002Fzyxel-firmware-decryption) article.","\u003Cp>The article introduces two methods: first, decrypting ZIP files via a known-plaintext attack using tools like pkcrack; second, obtaining the ZIP encryption password by tracking process parameters with `strace` on a MIPS-emulated environment where `zld_fsextract` runs. Both methods are detailed in the [Zyxel Firmware Decryption](\u002Fnews\u002Fzyxel-firmware-decryption) article.\u003C\u002Fp>\u003Cp>\u003Ca href=\"\u002Fnews\u002Fzyxel-firmware-decryption\">Read the related One Day Sec article\u003C\u002Fa>\u003C\u002Fp>","what-are-the-two-general-methods-for-decrypting-zyxel-firmware-discussed-in-the--1777481155439","Zyxel firmware decryption, known-plaintext attack, pkcrack, strace, zld_fsextract, MIPS",{"id":11,"title":12,"slug":13,"description":14,"content":15,"contentHtml":30,"cover":31,"author":32,"views":19,"readingTime":33,"status":34,"publishedAt":35,"seo":36,"tags":41,"qaPairs":42,"meta":47,"updatedAt":48,"createdAt":49,"_status":50},231,"Zyxel Firmware Decryption","zyxel-firmware-decryption","Learn two Zyxel firmware decryption methods: known plaintext attack (pkcrack) & password extraction via process tracking (zld_fsextract). Step-by-step insights for VPN50 firmware included.",{"root":16},{"type":17,"format":18,"indent":19,"version":20,"children":21,"direction":29},"root","",0,1,[22],{"type":23,"format":18,"indent":19,"version":20,"children":24,"direction":29},"paragraph",[25],{"mode":26,"text":27,"type":28,"style":18,"detail":19,"format":19,"version":20},"normal","\u003Chtml>\u003Chead>\u003C\u002Fhead>\u003Cbody>\u003Cp>Introduction: This article introduces two general methods for Zyxel firmware decryption and shares details that need to be recorded during the decryption process.\u003C\u002Fp>\u003Cp>\u003Cstrong>0x00 Preface\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>This article will introduce two general methods for Zyxel firmware decryption and record test insights.\u003C\u002Fp>\u003Cp>\u003Cstrong>0x01 Overview\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>This article will cover the following content:\u003C\u002Fp>\u003Cp>Basic Knowledge\u003C\u002Fp>\u003Cp>Decrypting ZIP Files via Known Plaintext Attack\u003C\u002Fp>\u003Cp>Obtaining ZIP Encryption Passwords by Tracking Process Parameters\u003C\u002Fp>\u003Cp>\u003Cstrong>0x02 Basic Knowledge\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>\u003Cstrong>1. Firmware Download\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>Firmware download address: https:\u002F\u002Fportal.myzyxel.com\u002Fmy\u002Ffirmwares\u003C\u002Fp>\u003Cp>An account registration is required to download the specified version of the firmware.\u003C\u002Fp>\u003Cp>\u003Cstrong>2. Common Firmware Types\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>ATP\u003C\u002Fp>\u003Cp>USG FLEX\u003C\u002Fp>\u003Cp>VPN\u003C\u002Fp>\u003Cp>ZyWALL\u002FUSG\u003C\u002Fp>\u003Cp>Here we take VPN50 5.36(ABHL.0) as an example; after downloading, save it as VPN50_V5.36(ABHL.0).zip\u003C\u002Fp>\u003Cp>Next, we introduce two methods for firmware decryption\u003C\u002Fp>\u003Cp>\u003Cstrong>0x03 Decrypting zip files via known-plaintext attack\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>References: https:\u002F\u002Fattackerkb.com\u002Ftopics\u002FN3i8dxpFKS\u002Fcve-2023-28771\u002Frapid7-analysis\u003C\u002Fp>\u003Cp>The file contents in VPN50_V5.36(ABHL.0).zip are as follows:\u003C\u002Fp>\u003Cp>536ABHL0C0.bin\u003C\u002Fp>\u003Cp>536ABHL0C0.conf\u003C\u002Fp>\u003Cp>536ABHL0C0.db\u003C\u002Fp>\u003Cp>536ABHL0C0.pdf\u003C\u002Fp>\u003Cp>536ABHL0C0.ri\u003C\u002Fp>\u003Cp>VPN50_V5.36(ABHL.0)C0-foss.pdf\u003C\u002Fp>\u003Cp>Among these, 536ABHL0C0.bin and 536ABHL0C0.db are encrypted and need to be decrypted\u003C\u002Fp>\u003Cp>Decryption Conditions:\u003C\u002Fp>\u003Cp>1. The complete plaintext file and zip file are known\u003C\u002Fp>\u003Cp>2. The plaintext file needs to be compressed using the same compression algorithm\u003C\u002Fp>\u003Cp>3. The encryption algorithm is ZipCrypto Store\u003C\u002Fp>\u003Cp>For VPN50_V5.36(ABHL.0).zip, the 536ABHL0C0.conf file is consistent with the db\u002Fetc\u002Fzyxel\u002Fftp\u002Fconf\u002Fsystem-default.conf file in 536ABHL0C0.bin and the etc\u002Fzyxel\u002Fftp\u002Fconf\u002Fsystem-default.conf file in 536ABHL0C0.db, which satisfies Condition 1\u003C\u002Fp>\u003Cp>Regarding Condition 2, it is necessary to determine the compression algorithms of 536ABHL0C0.bin and 536ABHL0C0.db. The reference materials do not cover this part either, so the analysis process is detailed here\u003C\u002Fp>\u003Cp>Check the compression information of db\u002Fetc\u002Fzyxel\u002Fftp\u002Fconf\u002Fsystem-default.conf in 536ABHL0C0.bin: zipdetails -v 536ABHL0C0.bin\u003C\u002Fp>\u003Cp>Return Result:\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_257\" src=\"\u002Fuploads\u002Fdocx_image_1769353523648_0_8225534d12.png\">\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_258\" src=\"\u002Fuploads\u002Fdocx_image_1769353527107_1_33697c31bc.png\">The compression algorithm obtained is as follows:\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_259\" src=\"\u002Fuploads\u002Fdocx_image_1769353527949_2_a4f8ad95d3.png\">\u003C\u002Fp>\u003Cp>Therefore, when compressing 536ABHL0C0.conf, the parameter -9 needs to be added to set it to 'compress better', i.e., Maximum Compression\u003C\u002Fp>\u003Cp>The complete decryption commands are as follows:\u003C\u002Fp>\u003Cp>\u003Cstrong>(1) Install pkcrack\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_260\" src=\"\u002Fuploads\u002Fdocx_image_1769353528350_3_b43d58417c.png\">\u003C\u002Fp>\u003Cp>\u003Cstrong>(2) Decrypt 536ABHL0C0.bin\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_261\" src=\"\u002Fuploads\u002Fdocx_image_1769353528923_4_f84cd8debf.png\">\u003C\u002Fp>\u003Cp>\u003Cstrong>(3) Decrypt 536ABHL0C0.db\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_262\" src=\"\u002Fuploads\u002Fdocx_image_1769353529796_5_ecc35c9955.png\">\u003C\u002Fp>\u003Cp>Note that the absolute paths of system-default.conf in 536ABHL0C0.bin and 536ABHL0C0.db are different\u003C\u002Fp>\u003Cp>\u003Cstrong>0x04 Obtaining zip encryption password by tracking process parameters\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>Reference: https:\u002F\u002Fsecurity.humanativaspa.it\u002Fzyxel-firmware-extraction-and-password-analysis\u002F\u003C\u002Fp>\u003Cp>Decryption principle: zld_fsextract can be extracted from .ri files, and zld_fsextract can calculate the decompression password based on the file content to decrypt the .bin file\u003C\u002Fp>\u003Cp>After testing, using zld_fsextract can also unlock .bin files of other firmwares\u003C\u002Fp>\u003Cp>\u003Cstrong>1. Extract zld_fsextract\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_263\" src=\"\u002Fuploads\u002Fdocx_image_1769353530285_6_93dc4b1a95.png\">\u003C\u002Fp>\u003Cp>Check file type: file zld_fsextract\u003C\u002Fp>\u003Cp>Return result: zld_fsextract: ELF 32-bit MSB executable, MIPS, N32 MIPS64 rel2 version 1 (SYSV), statically linked, stripped\u003C\u002Fp>\u003Cp>It indicates that zld_fsextract is of MIPS architecture, so a MIPS environment needs to be set up to run it\u003C\u002Fp>\u003Cp>\u003Cstrong>2. Set up MIPS environment\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_264\" src=\"\u002Fuploads\u002Fdocx_image_1769353530816_7_76e53356f3.png\">\u003C\u002Fp>\u003Cp>\u003Cstrong>3. Monitor process startup\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_265\" src=\"\u002Fuploads\u002Fdocx_image_1769353531395_8_d34315dd41.png\">\u003C\u002Fp>\u003Cp>Note:\u003C\u002Fp>\u003Cp>Need to add parameter -f to track child processes generated by fork calls, add parameter -s 199 to specify the length of the output string per line in the trace result; if parameter -s is not set, the complete decryption password cannot be recorded\u003C\u002Fp>\u003Cp>Return result example:\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_266\" src=\"\u002Fuploads\u002Fdocx_image_1769353531770_9_27b3fb4e3a.png\">\u003C\u002Fp>\u003Cp>Obtain the decryption password GfmirkjRUJla2evWFLtqJoI5a6vfOmDgR\u002FOIl7lFSWrXBm3S7yJTmdaMlV19HGr from it\u003C\u002Fp>\u003Cp>Note:\u003C\u002Fp>\u003Cp>This decryption password does not apply to 536ABHL0C0.db\u003C\u002Fp>\u003Cp>\u003Cstrong>0x05 Summary\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>This article introduces two general methods for decrypting Zyxel firmware and shares the details that need to be recorded during the decryption process.\u003C\u002Fp>\u003C\u002Fbody>\u003C\u002Fhtml>","text","ltr","\u003Chtml>\u003Chead>\u003C\u002Fhead>\u003Cbody>\u003Cp>Introduction: This article introduces two general methods for Zyxel firmware decryption and shares details that need to be recorded during the decryption process.\u003C\u002Fp>\u003Cp>\u003Cstrong>0x00 Preface\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>This article will introduce two general methods for Zyxel firmware decryption and record test insights.\u003C\u002Fp>\u003Cp>\u003Cstrong>0x01 Overview\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>This article will cover the following content:\u003C\u002Fp>\u003Cp>Basic Knowledge\u003C\u002Fp>\u003Cp>Decrypting ZIP Files via Known Plaintext Attack\u003C\u002Fp>\u003Cp>Obtaining ZIP Encryption Passwords by Tracking Process Parameters\u003C\u002Fp>\u003Cp>\u003Cstrong>0x02 Basic Knowledge\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>\u003Cstrong>1. Firmware Download\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>Firmware download address: https:\u002F\u002Fportal.myzyxel.com\u002Fmy\u002Ffirmwares\u003C\u002Fp>\u003Cp>An account registration is required to download the specified version of the firmware.\u003C\u002Fp>\u003Cp>\u003Cstrong>2. Common Firmware Types\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>ATP\u003C\u002Fp>\u003Cp>USG FLEX\u003C\u002Fp>\u003Cp>VPN\u003C\u002Fp>\u003Cp>ZyWALL\u002FUSG\u003C\u002Fp>\u003Cp>Here we take VPN50 5.36(ABHL.0) as an example; after downloading, save it as VPN50_V5.36(ABHL.0).zip\u003C\u002Fp>\u003Cp>Next, we introduce two methods for firmware decryption\u003C\u002Fp>\u003Cp>\u003Cstrong>0x03 Decrypting zip files via known-plaintext attack\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>References: https:\u002F\u002Fattackerkb.com\u002Ftopics\u002FN3i8dxpFKS\u002Fcve-2023-28771\u002Frapid7-analysis\u003C\u002Fp>\u003Cp>The file contents in VPN50_V5.36(ABHL.0).zip are as follows:\u003C\u002Fp>\u003Cp>536ABHL0C0.bin\u003C\u002Fp>\u003Cp>536ABHL0C0.conf\u003C\u002Fp>\u003Cp>536ABHL0C0.db\u003C\u002Fp>\u003Cp>536ABHL0C0.pdf\u003C\u002Fp>\u003Cp>536ABHL0C0.ri\u003C\u002Fp>\u003Cp>VPN50_V5.36(ABHL.0)C0-foss.pdf\u003C\u002Fp>\u003Cp>Among these, 536ABHL0C0.bin and 536ABHL0C0.db are encrypted and need to be decrypted\u003C\u002Fp>\u003Cp>Decryption Conditions:\u003C\u002Fp>\u003Cp>1. The complete plaintext file and zip file are known\u003C\u002Fp>\u003Cp>2. The plaintext file needs to be compressed using the same compression algorithm\u003C\u002Fp>\u003Cp>3. The encryption algorithm is ZipCrypto Store\u003C\u002Fp>\u003Cp>For VPN50_V5.36(ABHL.0).zip, the 536ABHL0C0.conf file is consistent with the db\u002Fetc\u002Fzyxel\u002Fftp\u002Fconf\u002Fsystem-default.conf file in 536ABHL0C0.bin and the etc\u002Fzyxel\u002Fftp\u002Fconf\u002Fsystem-default.conf file in 536ABHL0C0.db, which satisfies Condition 1\u003C\u002Fp>\u003Cp>Regarding Condition 2, it is necessary to determine the compression algorithms of 536ABHL0C0.bin and 536ABHL0C0.db. The reference materials do not cover this part either, so the analysis process is detailed here\u003C\u002Fp>\u003Cp>Check the compression information of db\u002Fetc\u002Fzyxel\u002Fftp\u002Fconf\u002Fsystem-default.conf in 536ABHL0C0.bin: zipdetails -v 536ABHL0C0.bin\u003C\u002Fp>\u003Cp>Return Result:\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_257\" src=\"\u002Fapi\u002Fmedia\u002Ffile\u002Fdocx_image_1769353523648_0_8225534d12-1.png\">\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_258\" src=\"\u002Fapi\u002Fmedia\u002Ffile\u002Fdocx_image_1769353527107_1_33697c31bc-1.png\">The compression algorithm obtained is as follows:\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_259\" src=\"\u002Fapi\u002Fmedia\u002Ffile\u002Fdocx_image_1769353527949_2_a4f8ad95d3-1.png\">\u003C\u002Fp>\u003Cp>Therefore, when compressing 536ABHL0C0.conf, the parameter -9 needs to be added to set it to 'compress better', i.e., Maximum Compression\u003C\u002Fp>\u003Cp>The complete decryption commands are as follows:\u003C\u002Fp>\u003Cp>\u003Cstrong>(1) Install pkcrack\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_260\" src=\"\u002Fapi\u002Fmedia\u002Ffile\u002Fdocx_image_1769353528350_3_b43d58417c-1.png\">\u003C\u002Fp>\u003Cp>\u003Cstrong>(2) Decrypt 536ABHL0C0.bin\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_261\" src=\"\u002Fapi\u002Fmedia\u002Ffile\u002Fdocx_image_1769353528923_4_f84cd8debf-1.png\">\u003C\u002Fp>\u003Cp>\u003Cstrong>(3) Decrypt 536ABHL0C0.db\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_262\" src=\"\u002Fapi\u002Fmedia\u002Ffile\u002Fdocx_image_1769353529796_5_ecc35c9955-1.png\">\u003C\u002Fp>\u003Cp>Note that the absolute paths of system-default.conf in 536ABHL0C0.bin and 536ABHL0C0.db are different\u003C\u002Fp>\u003Cp>\u003Cstrong>0x04 Obtaining zip encryption password by tracking process parameters\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>Reference: https:\u002F\u002Fsecurity.humanativaspa.it\u002Fzyxel-firmware-extraction-and-password-analysis\u002F\u003C\u002Fp>\u003Cp>Decryption principle: zld_fsextract can be extracted from .ri files, and zld_fsextract can calculate the decompression password based on the file content to decrypt the .bin file\u003C\u002Fp>\u003Cp>After testing, using zld_fsextract can also unlock .bin files of other firmwares\u003C\u002Fp>\u003Cp>\u003Cstrong>1. Extract zld_fsextract\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_263\" src=\"\u002Fapi\u002Fmedia\u002Ffile\u002Fdocx_image_1769353530285_6_93dc4b1a95-1.png\">\u003C\u002Fp>\u003Cp>Check file type: file zld_fsextract\u003C\u002Fp>\u003Cp>Return result: zld_fsextract: ELF 32-bit MSB executable, MIPS, N32 MIPS64 rel2 version 1 (SYSV), statically linked, stripped\u003C\u002Fp>\u003Cp>It indicates that zld_fsextract is of MIPS architecture, so a MIPS environment needs to be set up to run it\u003C\u002Fp>\u003Cp>\u003Cstrong>2. Set up MIPS environment\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_264\" src=\"\u002Fapi\u002Fmedia\u002Ffile\u002Fdocx_image_1769353530816_7_76e53356f3-1.png\">\u003C\u002Fp>\u003Cp>\u003Cstrong>3. Monitor process startup\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_265\" src=\"\u002Fapi\u002Fmedia\u002Ffile\u002Fdocx_image_1769353531395_8_d34315dd41-1.png\">\u003C\u002Fp>\u003Cp>Note:\u003C\u002Fp>\u003Cp>Need to add parameter -f to track child processes generated by fork calls, add parameter -s 199 to specify the length of the output string per line in the trace result; if parameter -s is not set, the complete decryption password cannot be recorded\u003C\u002Fp>\u003Cp>Return result example:\u003C\u002Fp>\u003Cp>\u003Cimg alt=\"IMG_266\" src=\"\u002Fapi\u002Fmedia\u002Ffile\u002Fdocx_image_1769353531770_9_27b3fb4e3a-1.png\">\u003C\u002Fp>\u003Cp>Obtain the decryption password GfmirkjRUJla2evWFLtqJoI5a6vfOmDgR\u002FOIl7lFSWrXBm3S7yJTmdaMlV19HGr from it\u003C\u002Fp>\u003Cp>Note:\u003C\u002Fp>\u003Cp>This decryption password does not apply to 536ABHL0C0.db\u003C\u002Fp>\u003Cp>\u003Cstrong>0x05 Summary\u003C\u002Fstrong>\u003C\u002Fp>\u003Cp>This article introduces two general methods for decrypting Zyxel firmware and shares the details that need to be recorded during the decryption process.\u003C\u002Fp>\u003C\u002Fbody>\u003C\u002Fhtml>",584,"Onedaysec",3,"published","2026-02-02T07:25:20.010Z",{"title":37,"description":14,"keywords":38,"ogImage":39,"canonicalUrl":39,"noIndex":40},"Zyxel Firmware Decryption: 2 Methods & Key Details","Zyxel firmware decryption, known plaintext attack, process parameter tracking, Zyxel firmware password, pkcrack, zld_fsextract, VPN50 firmware decryption",null,false,[],{"docs":43,"hasNextPage":40},[44,45,46,4],948,947,946,{"title":39,"description":39,"image":39},"2026-07-24T15:37:10.627Z","2026-07-23T16:02:18.873Z","draft","2026-07-23T16:15:42.694Z"]