Packagist supply-chain wave: Laravel-Lang autoloader backdoor and the cross-ecosystem postinstall strand

Background. The 2026 software supply chain has absorbed a sustained run of registry- and repo-level compromises — the mini-shai-hulud / TeamPCP npm/PyPI worm, the Megalodon GitHub-repo backdooring campaign (covered 2026-05-23), and the actions-cool/issues-helper GitHub Action and nx-console VS Code extension compromises (covered 2026-05-20). Those targeted npm, PyPI and CI tooling; the Packagist (PHP/Composer) ecosystem had largely escaped. Between 2026-05-22 and 2026-05-23 that changed, in two technically distinct, concurrent strands with different delivery mechanics — each flagged within hours by Socket, Aikido and StepSecurity (Socket, 2026-05-23). Socket reports the postinstall strand alone spans 700+ associated GitHub repositories under common attacker infrastructure (Socket, 2026-05-22); whether a single operator runs both strands is not established by the cited reporting.

Strand 1 — Laravel-Lang tag rewrite + autoloader backdoor. An actor with organisation-level push access to the Laravel-Lang GitHub org rewrote more than 700 historical version tags across four community PHP localisation packages — laravel-lang/lang (~7.8k stars), laravel-lang/http-statuses, laravel-lang/attributes, laravel-lang/actions. Rather than committing to the canonical repos, the attacker pointed existing version tags at commits in attacker-controlled forks, so the malicious code never appears in the main repository's commit history (StepSecurity, 2026-05-22). The injected src/helpers.php is registered under each composer.json's autoload.files key. Because every Composer application executes require __DIR__.'/vendor/autoload.php' at boot — Laravel, Symfony and PHPUnit included — the backdoor runs on every request with no post-install step required. A per-host MD5 fingerprint (directory path + architecture + inode) makes the payload fire once per machine to evade redundant-execution detection. The dropper builds its command-and-control hostname at runtime from character-code arrays (array_map('chr', …)) to defeat static string analysis, disables TLS certificate verification, spoofs a browser User-Agent, and fetches a ~5,900-line PHP credential stealer, which it writes to a hidden temp file and runs via exec("php …") on Unix or a VBScript-plus-cscript chain on Windows (Socket, 2026-05-23). The stealer is organised into fifteen collector modules targeting saved passwords from multiple Chromium-based browsers, Google Cloud application-default credentials, Docker auth tokens, SSH private keys, Git credentials (.gitconfig, .git-credentials, .netrc), shell and database history, kubeconfig, .env, wp-config.php, docker-compose.yml, VPN configurations, cryptocurrency wallets and password-manager vaults; results are AES-256-encrypted, exfiltrated, and the stealer self-deletes (Aikido, 2026-05-23).

Strand 2 — eight packages, cross-ecosystem postinstall. A concurrent campaign poisoned eight Packagist packages — devdojo/wave, devdojo/genesis, katanaui/katana, elitedevsquad/sidecar-laravel, r2luna/brain, baskarcm/tzi-chat-ui, moritz-sauer-13/silverstripe-cms-theme and crosiersource/crosierlib-base — by inserting a malicious hook into package.json (not composer.json) scripts.postinstall (Socket, 2026-05-22). The cross-ecosystem placement is deliberate: teams auditing PHP/Composer dependencies routinely skip the package.json lifecycle hooks bundled alongside JS build tooling. The hook downloads a Linux ELF from a code-hosting release URL, writes it to a hidden executable file under /tmp masquerading as an SSH daemon (e.g. /tmp/.sshd), marks it executable and launches it in the background with TLS verification suppressed and error output silenced (The Hacker News, 2026-05-23). The eight span CMS themes and developer libraries — including a SilverStripe CMS theme (moritz-sauer-13/silverstripe-cms-theme) and the crosiersource/crosierlib-base library — so the blast radius reaches any PHP project that pulled them as a direct or transitive dependency.

Kill chain → MITRE ATT&CK. Initial access and execution map to T1195.002 (Compromise Software Supply Chain) and T1059.004 (Unix Shell, via exec/postinstall); the runtime C2-hostname assembly and AES-256 output to T1140 (Deobfuscate/Decode Information); the /tmp/.sshd naming to T1036.005 (Masquerading: Match Legitimate Name or Location); the stealer's harvesting to T1552.001 (Credentials in Files) and T1083 (File and Directory Discovery); and the JS-side delivery to T1204.002 (User Execution: Malicious File).

Detection concepts (no IOCs). Audit composer.lock for any of the four laravel-lang/* packages at versions tagged in the 2026-05-22 → 2026-05-23 window, and for the eight named Strand-2 packages. Flag any autoload.files entry introduced by a version-tag change that has no counterpart in the package's upstream git history, and treat any scripts.postinstall / scripts.preinstall hook inside a PHP-only Composer package as a high-fidelity anomaly. On hosts and CI runners, hunt (Sysmon EID 1 / Linux auditd) for web-server worker processes (php-fpm, php-cgi, apache2, nginx) spawning exec("php …") or cscript.exe, for composer/npm spawning shells or initiating network connections during install, and for an executable hidden file under /tmp resembling sshd. Egress monitoring: outbound HTTPS from PHP worker processes during autoload, and installs pulling binaries from code-hosting release CDNs during composer/npm install.

Hardening. Run composer audit (Composer 2.6+), pin exact dependency versions, and verify composer.lock hash integrity in CI. Review whether organisation-level GitHub token scoping permits tag rewrites across all repositories and rotate admin tokens if compromise is suspected. On any affected host, treat all secrets reachable by the PHP worker process — cloud keys, SSH keys, .env, Git tokens — as compromised and rotate aggressively. For the JS-tooling surface, adopt npm's new staged-publishing 2FA gate and --allow-remote none / --allow-directory none install controls (. Note that Packagist removed the malicious versions, but development branches stay infected while upstream GitHub repos remain compromised — verify upstream state before reinstalling any of the named packages.