GHSA-q6h5-q3q6-f87x BIT-cilium-2026-53935 BIT-cilium-operator-2026-53935 BIT-hubble-relay-2026-53935 CVE-2026-53935 GO-2026-5914

CiliumLocalRedirectPolicy addressMatcher allows cross-namespace service traffic hijacking and can break service translation

Medium Go

Severity: 6.9 / 10; Medium · CVSS 3.1
Exploit chance (EPSS): 0.34%; Chance of exploitation in the next 30 days. Higher than 27.54% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-601 URL Redirection to Untrusted Site ('Open Redirect')
Fix: 1.19.4; Upgrade github.com/cilium/cilium to this version or later

Description

Impact

Users with the ability to create CiliumLocalRedirectPolicies can specify arbitrary ClusterIPs via addressMatcher, which enables hijacking traffic to Services in any namespace, bypassing the namespace-scoping guarantees enforced by serviceMatcher.

In addition, deleting such a policy can corrupt Cilium's internal service state, causing service translation to stop working entirely for the affected Service.

Patches

This issue affects:

Cilium v1.19.0 to v1.19.3 inclusive (fixed in PR #45584)
Cilium v1.18.2 to v1.18.9 inclusive (fixed in PR #45585)
All versions of Cilium prior to v1.17.16 (fixed in PR #45412)

This issue has been patched in:

Cilium v1.19.4
Cilium v1.18.10
Cilium v1.17.16

Workarounds

There is no workaround to this issue.

Acknowledgements

The Cilium community has worked together with members of Isovalent to prepare these mitigations. Special thanks to @ysksuzuki for investigating and fixing the issue.

For more information

If there are any questions or comments about this advisory, please reach out on Slack.

To report potential vulnerabilities affecting Cilium, it strongly is encouraged to report them through the security mailing list at security@cilium.io. This is a private mailing list for the Cilium security team, and reports will be treated as a top priority.

Affected versions

Go

Package	Vulnerable	Fixed in
github.com/cilium/cilium	`>= 1.19.0, < 1.19.4`	`1.19.4`
github.com/cilium/cilium	`>= 1.18.2, < 1.18.10`	`1.18.10`
github.com/cilium/cilium	`< 1.17.16`	`1.17.16`
github.com/cilium/cilium	`< 1.17.16` `>= 1.18.2, < 1.18.10` `>= 1.19.0, < 1.19.4`	`1.17.16` `1.18.10` `1.19.4`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

github.com/cilium/cilium Go → `1.19.4`

go

go get github.com/cilium/cilium@v1.19.4 && go mod tidy

Severity breakdown

CVSS 3.1 6.9

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

Attack vector: Adjacent
Attack complexity: Low
Privileges required: High
User interaction: None
Scope: Changed
Confidentiality: Low
Integrity: None
Availability: High

Weakness

CWE-601: URL Redirection to Untrusted Site ('Open Redirect')

The web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a redirect.

How to prevent it

Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. Use a list of approved URLs or domains to be used for redirection.
Architecture and Design: Use an intermediate disclaimer page that provides the user with a clear warning that they are leaving the current site. Implement a long timeout before the redirect occurs, or force the user to click on the link. Be careful to avoid XSS problems (CWE-79) when generating the disclaimer page.
Architecture and Design: When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs. For example, ID 1 could map to "/login.asp" and ID 2 could map to "http://www.example.com/". Features such as the ESAPI AccessReferenceMap [REF-45] provide this capability.
Architecture and Design: Ensure that no externally-supplied requests are honored by requiring that all redirect requests include a unique nonce generated by the application [REF-483]. Be sure that the nonce is not predictable (CWE-330).
Architecture and Design, Implementation: Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls. Many open redirect problems occur because the programmer assumed that certain inputs could not be modified, such as cookies and hidden form fields.
Operation: Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].

References

Packages

github.com/cilium/cilium

Timeline

Jul 6, 2026 Published
Sep 10, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-fm8w-2m5w-9j7r Cilium may unexpectedly allow ingress traffic from the local namespace when a Kubernetes NetworkPolicy is configured with an ipBlock match	Medium	Also affects github.com/cilium/cilium
GHSA-w7c2-w76w-5hmj Cilium: Namespaced HTTPRoutes can redirect traffic to other namespaces	High	Also affects github.com/cilium/cilium
GHSA-3fcv-jvfp-m4q9 Cilium vulnerable to sensitive information disclosure and cluster disruption via local Envoy admin socket access	High	Also affects github.com/cilium/cilium
GHSA-gj49-89wh-h4gj Cillium exposes sensitive information included in the cilium-bugtool debug archive	Medium	Also affects github.com/cilium/cilium
GHSA-hxv8-4j4r-cqgv Cilium L7 proxy may bypass Kubernetes NetworkPolicy for same-node traffic	Medium	Also affects github.com/cilium/cilium
GHSA-5r23-prx4-mqg3 Cilium may not enforce host firewall policies when Native Routing, WireGuard and Node Encryption are enabled	Medium	Also affects github.com/cilium/cilium
GHSA-38pp-6gcp-rqvm Cilium with misconfigured toGroups in policies can lead to unrestricted egress traffic	Medium	Also affects github.com/cilium/cilium
GHSA-5vxx-c285-pcq4 In Cilium, packets from terminating endpoints may not be encrypted in Wireguard-enabled clusters	Medium	Also affects github.com/cilium/cilium

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