CVE-2026-59247

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in, but needs a user to act. High risk of data exposure, data tampering.

Exploit odds

0.2% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-07-29 15:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-10-23 23:10 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.2% in the next 30 days (EPSS).
• Severity: 7.6 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-07-29 15:16 UTC

Last modified

2026-10-23 23:10 UTC

Exploit probability

0.2% · EPSS, next 30 days

Weakness

CWE-345

Record status

Deferred

Attack profile CVSS 4.0 · 7.6

Attack vector

Network

Complexity

Low

Attack requirements

Present

Privileges needed

None

User interaction

Passive

Confidentiality

High

Integrity

High

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-59247.md and follow it. Check whether this project is affected by CVE-2026-59247. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

Copy as ticket · More options · Status badge