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daily-triage/branch-based-cache-key-reintroduces-patched-ci-cd-dependency.md
Daily Triage Briefing

A Branch-Based Cache Key Reintroduces a Patched CI/CD Dependency

Impact Summary

A fictional triage exercise in which a CI/CD pipeline's cache key, built only from branch name and operating system, silently restores a pre-patch dependency tree on the main branch while feature branches appear correctly patched.

SeveritySEV-2
StatusResolved simulation
PlatformCI/CD & Developer Platforms
Incident TypeCI/CD & Developer Platforms
Published9 Aug 2026
Technologies Involved
CI/CD

Simulation Label

Fictional simulation. This exercise is a bounded, invented training scenario for practising operational reasoning. No real organisation, incident, telemetry, credentials or production identifiers are involved or implied.

Operational Summary

Root Cause

The pipeline's cache key was derived only from the branch name and operating system, with no component tied to the lockfile's content. Because the main branch's cache entry was created before a dependency patch merged, later runs on main matched the same key and restored the pre-patch dependency tree without reinstalling, while feature branches with new key values always performed a fresh install and appeared correctly patched.

Detection Method

Evidence-led guided investigation

Current Status

Resolved simulation

Affected Services

CI/CD

Incident Overview

A platform team maintains a shared CI/CD pipeline used by several internal services. Three days ago, a critical vulnerability in a widely used dependency was patched, the lockfile was updated, and the change was merged to the main branch.

Today, a routine vulnerability scan against a freshly built artefact from main still flags the old, vulnerable dependency version, even though the pipeline reports a fully green run with a successful cache restore step.

Investigation Options

Review the available operational moves and select the best immediate action.

A

Manually invalidate the affected cache entries and force a clean dependency install on the next pipeline run for the main branch.

B

Revert the dependency patch commit on main so its state matches what the cache currently restores.

C

Introduce a mandatory manual review step where an engineer confirms the installed dependency version before every deployment from main.

D

Disable caching for all pipelines across the organisation until the caching strategy can be redesigned.

Tags:CI/CD