CVE-2026-27959

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Last Modified: UTC

Important Important Impact What does this mean?
8.2 CVSS v3 Base Score

Description

A flaw was found in Koa’s ctx.hostname API used in Node.js applications. The function incorrectly parses specially crafted HTTP Host headers containing an @ character, which can cause the extracted hostname value to differ from the intended origin. An attacker can exploit this behavior by sending a malicious Host header to influence the hostname value returned by ctx.hostname. Applications that rely on this value for generating absolute URLs, password reset links, or email verification links without additional validation may be susceptible to Host header injection attacks.

Statement

Red Hat Product Security considers this issue as High severity.

A remote, unauthenticated attacker can send a specially crafted HTTP Host header containing a valid RFC 3986 userinfo component (using the @ delimiter). Due to improper parsing of the authority field in the ctx.hostname API, the application may treat attacker-controlled input as the hostname value. Exploitation occurs when the server processes the malicious request and does not require user interaction (UI:N).

Applications that rely on ctx.hostname to construct absolute URLs, such as: password reset links, email verification links, OAuth redirect URIs, or webhook endpoints, may generate security sensitive URLs that reference an attacker controlled domain. This can result in integrity violations, including manipulation of authentication flows or account takeover scenarios. Integrity impact is therefore rated High.

Confidentiality impact is considered Low because disclosure of sensitive data depends on application-specific usage patterns. The vulnerability does not automatically expose information from the server. However, if an affected application uses the manipulated hostname value to generate security-sensitive links such as password reset or email verification URLs and embeds tokens in those links without additional validation, a victim who later follows such a link may inadvertently disclose those tokens to an attacker controlled domain. Such disclosure is conditional, application-dependent like how the application constructs URLs. Also, the subsequent user interaction beyond the initial exploitation, the confidentiality impact is assessed as Low (C:L).

Mitigation

Red Hat is not aware of a practical temporary workaround that fully mitigates this issue or meets Red Hat Product Security's standards for usability, deployment, applicability, or stability. Customers are advised to apply the relevant security updates once they become available.

Additional Information

External References

Content from www.cve.org is not included.https://www.cve.org/CVERecord?id=CVE-2026-27959

Content from nvd.nist.gov is not included.https://nvd.nist.gov/vuln/detail/CVE-2026-27959

Content from github.com is not included.https://github.com/koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6df

Content from github.com is not included.https://github.com/koajs/koa/commit/b76ddc01fdb703e51652b0fd131d16394cadcfeb

Content from github.com is not included.https://github.com/koajs/koa/security/advisories/GHSA-7gcc-r8m5-44qm

Affected Packages and Issued Red Hat Security Errata

Products / Services Components State Errata
Red Hat Developer Hub rhdh/rhdh-hub-rhel9 Will not fix
Red Hat OpenShift AI (RHOAI) rhoai/odh-mod-arch-gen-ai-rhel9 Out of support scope
Red Hat OpenShift AI 2.25 rhoai/odh-dashboard-rhel9 Fixed RHSA-2026:10184
Red Hat OpenShift AI 2.25 rhoai/odh-mod-arch-model-registry-rhel9 Fixed RHSA-2026:10184
Red Hat OpenShift Container Platform 4.19 openshift4/ose-monitoring-plugin-rhel9 Fixed RHSA-2026:7249
Red Hat OpenShift Dev Spaces devspaces/code-rhel9 Not affected
Self-service automation portal 2 ansible-automation-platform/automation-portal Affected
Unless explicitly stated as not affected, all previous versions of packages in any minor update stream of a product listed here should be assumed vulnerable, although may not have been subject to full analysis.

Common Vulnerability Scoring System (CVSS) Score Details

Important note

CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authorities (CNA) source for its products and services (see Red Hat classifications ).

CVSS v3 Score Breakdown Red Hat NVD
CVSS v3 Base Score 8.2
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope Unchanged
Confidentiality Impact Low
Integrity Impact High
Availability Impact None

CVSS v3 Vector

Red Hat CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N

Frequently Asked Questions

Why is Red Hat's CVSS v3 score or Impact different from other vendors?

 For open source software shipped by multiple vendors, the CVSS base scores may vary for each vendor's version depending on the version they ship, how they ship it, the platform, and even how the software is compiled. This makes scoring of vulnerabilities difficult for third-party vulnerability databases such as NVD that only provide a single CVSS base score for each vulnerability. Red Hat scores reflect how a vulnerability affects our products specifically.

For more information, see https://access.redhat.com/solutions/762393.

My product is listed as "Under investigation" or "Affected", when will Red Hat release a fix for this vulnerability?
  • "Under investigation" doesn't necessarily mean that the product is affected by this vulnerability. It only means that our Analysis Team is still working on determining whether the product is affected and how it is affected.
  • "Affected" means that our Analysis Team has determined that this product is affected by this vulnerability and might release a fix to address this in the near future.

What can I do if my product is listed as "Will not fix"?

 A "will not fix" status means that a fix for an affected product version is not planned or not possible due to complexity, which may create additional risk.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Upgrade to a supported product version that includes a fix for this vulnerability (recommended).
  • Apply a mitigation (if one exists).
  • Open a This content is not included.support case to request a prioritization of releasing a fix for this vulnerability.

What can I do if my product is listed as "Fix deferred"?

 A deferred status means that a fix for an affected product version is not guaranteed due to higher-priority development work.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Apply a mitigation (if one exists).
  • Open a This content is not included.support case to request a prioritization of releasing a fix for this vulnerability.
  • Red Hat Engineering focuses on addressing high-priority issues based on their complexity or limited lifecycle support. Therefore, lower-priority issues will not receive immediate fixes.

What is a mitigation?

 A mitigation is an action that can be taken to reduce the impact of a security vulnerability, without deploying any fixes.

I have a Red Hat product but it is not in the above list, is it affected?

 The listed products were found to include one or more of the components that this vulnerability affects. These products underwent a thorough evaluation to determine their affectedness by this vulnerability. Note that layered products (such as container-based offerings) that consume affected components from any of the products listed in this table may be affected and are not represented.

Why is my security scanner reporting my product as vulnerable to this vulnerability even though my product version is fixed or not affected?

 In order to maintain code stability and compatibility, Red Hat usually does not rebase packages to entirely new versions. Instead, we backport fixes and new features to an older version of the package we distribute. This can result in some security scanners that only consider the package version to report the package as vulnerable. To avoid this, we suggest that you use an approved vulnerability scanner from our This content is not included.Red Hat Vulnerability Scanner Certification program.

My product is listed as "Out of Support Scope". What does this mean?

 When a product is listed as "Out of Support Scope", it means a vulnerability with the impact level assigned to this CVE is no longer covered by its current support lifecycle phase. The product has been identified to contain the impacted component, but analysis to determine whether it is affected or not by this vulnerability was not performed. The product should be assumed to be affected. Customers are advised to apply any mitigation options documented on this page, consider removing or disabling the impacted component, or upgrade to a supported version of the product that has an update available.