RubyGems fails to re-validate path containment after filesystem symlink resolution during gem extraction. When a pre-existing symlink inside the destination directory points outside the extraction root, extracted files that appear to be written under the destination directory can instead be written outside of it, breaking the extraction safety boundary. The fix resolves the real path of the parent directory before writing and raises Gem::Package::PathError if it escapes the destination directory.
Casky was already ahead
This CVE exploits attack patterns that Casky's 0matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.
CVE-2026-82455 exposes a critical path traversal vulnerability in RubyGems where pre-existing symlinks within extraction directories can be exploited to write files outside the intended destination root. This vulnerability allows attackers to bypass security boundaries during gem extraction, potentially enabling arbitrary file write operations on affected systems. The issue affects any developer or system relying on RubyGems for package management, particularly in automated build pipelines, containerized environments, and supply chain scenarios where malicious gems could be leveraged to compromise host systems or inject code into downstream dependencies.
While this CVE currently maps to zero Casky security skills due to its specificity to RubyGems internals, practitioners using Casky's platform would detect the exploitation patterns associated with this vulnerability through monitoring techniques aligned with CWE-59 (Improper Link Resolution Before File Access). Claude AI's extended reasoning capabilities within Casky enable detection of anomalous file system operations—such as unusual symlink creation followed by package extraction attempts, or file writes to unexpected paths outside declared package boundaries. Security teams would observe indicators like failed path validation checks, Gem::Package::PathError exceptions in logs, or suspicious file system activity during gem installation phases. By analyzing extraction logs and file system events through Casky's threat intelligence framework, practitioners can identify attempted exploitation of this path traversal flaw before malicious files reach their destinations.
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