CVE-2026-77866: Software Security Vulnerability Vulnerability

CRITICAL
Advisory Identifier: GHSA-97fv-h8pq-9grg
Share
CWE-636
Published
Advisory Summary

CVE-2026-77866 is a CRITICAL security vulnerability vulnerability (CWE-636: Not Failing Securely ('Failing Open')) affecting Software libraries in the Maven ecosystem. The weakness occurs when when the product encounters an error condition or failure, its design requires it to fall back to a state that is less secure than other options that are available, such as selecting the weakest encryption algorithm or using the most permissive access control restrictions.. Remediation is available in the latest vendor maintenance releases.

CVE-2026-77866 at a Glance

CVE Identifier CVE-2026-77866
GHSA Identifier GHSA-97fv-h8pq-9grg
Severity CRITICAL
CVSS v3.1 Base Score N/A
CWE Classification CWE-636: Not Failing Securely ('Failing Open')
Affected Product Software
Package Ecosystem Maven
Published Date
Last Updated

How to Fix CVE-2026-77866

To remediate this vulnerability, upgrade all affected Software dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

mvn dependency:tree

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2026-77866, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree

Analyze the terminal output to locate any version of Software in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: The mvn dependency:tree command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-636: Not Failing Securely ('Failing Open'), where when the product encounters an error condition or failure, its design requires it to fall back to a state that is less secure than other options that are available, such as selecting the weakest encryption algorithm or using the most permissive access control restrictions. In Software, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

Server-Side Request Forgery (SSRF) vulnerability in Slab safeurl allows an attacker who controls a validated URL to reach internal network destinations the library is configured to block. Only IPv4 addresses are matched against the reserved ranges and the blocklist. Every other address is treated as matching nothing, so a destination that is rejected in its IPv4 form is accepted when written as an IPv6 address, IPv6 entries in the blocklist never match, and a host that resolves to no IPv4 address is accepted regardless of where it points. Deployments that rely on the allowlist instead are unaffected, because there an unmatched address is rejected. This issue affects safeurl: from 0.1.0 onward.

References

NVD — CVE-2026-77866 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-77866
Security Fix Commit FIX COMMIT
https://github.com/slab/safeurl-elixir/commit/feabbd0a13f83028ab24b71710526e9da9841f70
cna.erlef.org/cves/cve-2026-77866... WEB
https://cna.erlef.org/cves/CVE-2026-77866.html
osv.dev/vulnerability/eef-c... WEB
https://osv.dev/vulnerability/EEF-CVE-2026-77866

Frequently Asked Questions

What is CVE-2026-77866?
CVE-2026-77866 is a security vulnerability in Software classified as a security vulnerability vulnerability under CWE-636: Not Failing Securely ('Failing Open').
Which Software versions are affected?
Affected versions include releases prior to current release patches.
What version fixes CVE-2026-77866?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
What CWE is associated with CVE-2026-77866?
CVE-2026-77866 is classified under CWE-636: Not Failing Securely ('Failing Open') (When the product encounters an error condition or failure, its design requires it to fall back to a state that is less secure than other options that are available, such as selecting the weakest encryption algorithm or using the most permissive access control restrictions.).
How can I check Maven dependencies for CVE-2026-77866?
Run the dependency tree command: 'mvn dependency:tree'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-97fv-h8pq-9grg",
  "modified" : "2026-09-15T18:32:26Z",
  "published" : "2026-09-15T18:32:26Z",
  "aliases" : [ "CVE-2026-77866" ],
  "details" : "Server-Side Request Forgery (SSRF) vulnerability in Slab safeurl allows an attacker who controls a validated URL to reach internal network destinations the library is configured to block.\n\nOnly IPv4 addresses are matched against the reserved ranges and the blocklist. Every other address is treated as matching nothing, so a destination that is rejected in its IPv4 form is accepted when written as an IPv6 address, IPv6 entries in the blocklist never match, and a host that resolves to no IPv4 address is accepted regardless of where it points. Deployments that rely on the allowlist instead are unaffected, because there an unmatched address is rejected.\n\nThis issue affects safeurl: from 0.1.0 onward.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:L/VA:N/SC:H/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"
  } ],
  "affected" : [ ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-77866"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/slab/safeurl-elixir/commit/feabbd0a13f83028ab24b71710526e9da9841f70"
  }, {
    "type" : "WEB",
    "url" : "https://cna.erlef.org/cves/CVE-2026-77866.html"
  }, {
    "type" : "WEB",
    "url" : "https://osv.dev/vulnerability/EEF-CVE-2026-77866"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-636" ],
    "severity" : "CRITICAL",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2026-09-15T16:17:24Z"
  }
}