AWS SAM CLI EUVD-2026-108281

Requires that the target actually uses the Terraform hook build mode (sam build --hook-name terraform) in AWS SAM CLI 1.63.0 through 1.166.1, AND that an attacker can influence the Terraform configuration or a Terraform plan file consumed by that build - typically via an untrusted or compromised third-party Terraform module, shared repository, or plan artifact. The payload is a crafted Terraform resource address of a SAM metadata resource containing shell metacharacters (e.g. command substitution), which the hook passes through because only double-quote characters were escaped. Exploitation is LOCAL to the build host (AV:L) and requires the build to be invoked (UI:A), but needs no AWS credentials and executes even if the build subsequently fails. Limiting factors: default SAM workflows that do not use the Terraform hook, or builds that consume only trusted first-party Terraform sources, are not exposed; the per-vendor workaround is to source Terraform config/plan files only from trusted sources and audit third-party modules, with upgrade to 1.166.2 as the recommended complete remediation.

This is a credible but conditional supply-chain/build-time risk rather than a mass-exploitable network flaw. The authoritative CVSS 4.0 vector (AV:L/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H) scores 8.4 and correctly models the mechanics: exploitation is Local (the malicious input is consumed by a build running on the host), requires Active user interaction (someone must invoke sam build --hook-name terraform), needs no privileges on the SAM CLI side (PR:N), and yields High impact to confidentiality, integrity and availability with no scope change. No EPSS score was supplied and the CVE is NOT in CISA KEV, so there is no_public_exploit identified at time of analysis and no evidence of active exploitation - treat the headline 8.4 as severity, not imminence. The vuln.today Decision label is 'this_week' (not act_now/emergency), consistent with a patched, credibly-impactful but not-yet-exploited issue. The signals are internally consistent: a serious code-execution bug gated behind the precondition that an attacker can influence the Terraform configuration or plan file. The realistic threat is poisoned third-party Terraform modules or shared repositories flowing into CI/CD, where command execution during the build exposes pipeline credentials and allows artifact tampering even if the build later fails.

An attacker contributes or compromises a Terraform module (or plan file) consumed by a target's build, embedding shell command-substitution syntax inside a Terraform resource address. When a developer or CI/CD pipeline runs sam build --hook-name terraform, the SAM CLI inserts that address into a shell command while neutralizing only double quotes, so the injected command executes as the build user - harvesting CI/CD credentials and tampering with artifacts. No public exploit is identified at time of analysis, but the GHSA advisory documents the mechanism in detail.