# CVE-2026-100837: Edgeless Systems Contrast through 1.20.0 Credential Leak via Registry Suffix Matching

> Attackers can steal registry credentials and bypass TLS verification by registering domains that match unanchored suffixes in Contrast configuration.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 Sep 2026
- **Updated:** 28 Sep 2026
- **Also known as:** GHSA-6c87-g9pw-78fx, GHSA-frqc-cxqj-qxmv, GO-2026-5865

## What is CVE-2026-100837?

CVE-2026-100837 is a medium-severity vulnerability in edgelesssys contrast, published on 27 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Contrast (Edgeless Systems) through 1.20.0 performs unanchored suffix matching when selecting per-registry configuration in the imagepuller. Config.registryFor strips a single trailing dot and then uses strings.HasSuffix(hostname, fqdn) without requiring a DNS label boundary, so a registry entry such as [registries."ghcr.io."] is also applied to any host whose name merely ends in that byte sequence, including attacker-registered domains such as evilghcr.io. When an image or layer is pulled from such a sibling domain, the imagepuller sends the configured Authorization header (basic auth, registry token, or identity token), trusts the configured custom CA bundle, follows the configured mirror, and honours insecure-skip-verify (disabling TLS verification) for that host. Image integrity is not affected, as image bytes remain pinned by digest in the policy and are validated after the pull. Configurations that use a leading dot (e.g., [registries.".example.registry"]) are unaffected.

Weakness: CWE-1289 (Improper Validation of Unsafe Equivalence in Input)

## Which versions are affected by CVE-2026-100837?

3 open source packages ship an affected version, including github.com/edgelesssys/contrast.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/edgelesssys/contrast` | Go | All versions | 1.21.0 |
| `github.com/edgelesssys/contrast` | Go | All versions | 1.21.0 |
| `github.com/edgelesssys/contrast` | Go | All versions | 1.21.0 |

## How do I fix CVE-2026-100837?

Upgrade github.com/edgelesssys/contrast to 1.21.0 or later.

## Is CVE-2026-100837 being exploited?

There is no known exploitation of CVE-2026-100837 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-100837 and fix it if it is affected.

What it is: CVE-2026-100837 is a medium-severity vulnerability in edgelesssys contrast, published on 27 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-100837 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/edgelesssys/contrast (Go): affected all versions; fixed in 1.21.0
- github.com/edgelesssys/contrast (Go): affected all versions; fixed in 1.21.0
- github.com/edgelesssys/contrast (Go): affected all versions; fixed in 1.21.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-100837/ (Markdown: https://insights.sbomify.com/CVE-2026-100837/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-100837
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-100837
- OSV: https://osv.dev/vulnerability/CVE-2026-100837

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-100837/
Summaries are generated and may contain mistakes; the official description above is the record.