CVE-2026-59247
CVE-2026-59247 is a CWE-345 vulnerability. O3 Security confirms whether CVE-2026-59247 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Insufficient Verification of Data Authenticity vulnerability in Gleam allows an adversary in the middle to substitute forged Hex package contents during dependency resolution. During…
Description
Insufficient Verification of Data Authenticity vulnerability in Gleam allows an adversary in the middle to substitute forged Hex package contents during dependency resolution.
During dependency resolution Gleam fetches package metadata from the signature-verified Hex repository, which covers each release's dependency requirements and SHA-256 outer_checksum. After resolving versions, gleam_cli::dependencies::lookup_package makes a second request to the unsigned Hex API through gleam_core::hex::get_package_release and records the outer_checksum and dependency names from that JSON response into manifest.toml, instead of the values from the verified repository metadata. The Hex repository signature does not cover the API response.
An adversary in the middle who can intercept TLS with a certificate trusted by the Gleam process (for example a TLS-inspecting proxy using a CA in the operating system trust store or added through GLEAM_CACERTS_PATH), and who can modify both the API release response and the corresponding repository tarball, can supply a package archive with a matching forged checksum without the Hex repository signing key. Gleam verifies the forged tarball against the forged checksum, accepts it, and extracts it as a dependency source, resulting in loss of integrity of the downloaded package contents.
Only projects that resolve or update Hex dependencies are affected, which happens when the manifest is missing, a dependency is added or updated, or dependency requirements change. Builds that reuse an unchanged, known-good manifest.toml continue to verify tarballs against its pinned checksum. This issue affects gleam: from 0.18.0 before 1.18.0.
Detection & mitigation playbook
VulnerabilityDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for the affected component. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Remediation status
No patched version of the affected component has shipped for CVE-2026-59247 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-59247 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-59247. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-59247 in your dependencies?
O3 detects CVE-2026-59247 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.