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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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
Which versions are affected by CVE-2026-100837?
3 open source packages ship an affected version, including github.com/edgelesssys/contrast.
| Package | 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.
Sources
Also known as GHSA-6c87-g9pw-78fx, GHSA-frqc-cxqj-qxmv, GO-2026-5865.