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Flannel is a network fabric for containers, designed for Kubernetes. The Flannel project includes an experimental Extension backend that allows users to easily prototype new backend types. In versions of Flannel prior to 0.28.2, this Extension backend is vulnerable to a command injection that allows an attacker who can set Kubernetes Node annotations to achieve root-level arbitrary command execution on every flannel node in the cluster. The Extension backend's SubnetAddCommand and SubnetRemoveCommand receive attacker-controlled data via stdin (from the `flannel.alpha.coreos.com/backend-data` Node annotation). The content of this annotation is unmarshalled and piped directly to a shell command without checks. Kubernetes clusters using Flannel with the Extension backend are affected by this vulnerability. Other backends such as vxlan and wireguard are unaffected. The vulnerability is fixed in version v0.28.2. As a workaround, use Flannel with another backend such as vxlan or wireguard.
Read the publisher's advisoryFlannel is a network fabric for containers, designed for Kubernetes. The Flannel project includes an experimental Extension backend that allows users to easily prototype new backend types. In versions of Flannel prior to 0.28.2, this Extension backend is vulnerable to a command injection that allows an attacker who can set Kubernetes Node annotations to achieve root-level arbitrary command execution on every flannel node in the cluster. The Extension backend's SubnetAddCommand and SubnetRemoveCommand receive attacker-controlled data via stdin (from the `flannel.alpha.coreos.com/backend-data` Node annotation). The content of this annotation is unmarshalled and piped directly to a shell command without checks. Kubernetes clusters using Flannel with the Extension backend are affected by this vulnerability. Other backends such as vxlan and wireguard are unaffected. The vulnerability is fixed in version v0.28.2. As a workaround, use Flannel with another backend such as vxlan or wireguard.
Read the publisher's advisoryFlannel is a network fabric for containers, designed for Kubernetes. The Flannel project includes an experimental Extension backend that allows users to easily prototype new backend types. In versions of Flannel prior to 0.28.2, this Extension backend is vulnerable to a command injection that allows an attacker who can set Kubernetes Node annotations to achieve root-level arbitrary command execution on every flannel node in the cluster. The Extension backend's SubnetAddCommand and SubnetRemoveCommand receive attacker-controlled data via stdin (from the `flannel.alpha.coreos.com/backend-data` Node annotation). The content of this annotation is unmarshalled and piped directly to a shell command without checks. Kubernetes clusters using Flannel with the Extension backend are affected by this vulnerability. Other backends such as vxlan and wireguard are unaffected. The vulnerability is fixed in version v0.28.2. As a workaround, use Flannel with another backend such as vxlan or wireguard.
Read the publisher's advisory### Background The Flannel project includes an experimental Extension backend that allows users to easily prototype new backend types. This backend uses shell commands stored in Kubernetes annotations to configure network connectivity on the node. Note: consumers are only affected by this vulnerability if they use the experimental Extension backend. Other backends such as vxlan and wireguard are unaffected. ### Vulnerability This Extension backend is vulnerable to a command injection that allows an attacker who can set Kubernetes Node annotations to achieve root-level arbitrary command execution on every flannel node in the cluster. The Extension backend's SubnetAddCommand and SubnetRemoveCommand receive attacker-controlled data via stdin (from the `flannel.alpha.coreos.com/backend-data` Node annotation). The content of this annotation is unmarshalled and piped directly to a shell command without checks. ### Impact Kubernetes clusters using Flannel with the Extension backend are affected by this vulnerability. Other backends such as vxlan and wireguard are unaffected. ### Patches This is fixed in version v0.28.2. ### Workaround If consumers cannot update to a patched version, then use Flannel with another backend such as vxlan or wireguard. ### Credits Flannel would like to thank Shachar Tal from Palo Alto Networks for reporting this vulnerability.
Read the publisher's advisoryFlannel has cross-node remote code execution via extension backend BackendData injection in github.com/flannel-io/flannel
Read the publisher's advisoryVendor product
Shown as published. These rules are not interpreted as NuGet package version ranges.
{
"vendor": "flannel-io",
"product": "flannel",
"versions": [
{
"version": "< 0.28.2",
"status": "affected"
}
]
}Original source record · Cite this exact observation · Complete original publisher JSON
EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.
datePublished: Mar 27, 2026, 7:31:48 PM
dateUpdated: Mar 31, 2026, 6:54:30 PM
msrc_CVE-2026-32241: Flannel vulnerable to cross-node remote code execution via extension backend BackendData injection
CVE-2026-32241
openSUSE-SU-2026:12270-1: flannel-0.28.10-1.1 on GA media
CVE-2024-51744 · CVE-2026-32241 · CVE-2026-46600 · CVE-2026-56852
No normalized affected-package data is projected for this source revision. The original publisher record may contain additional product and version evidence; this does not establish that a package is unaffected.
Original source record · Cite this exact observation · Complete original publisher JSON
NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.
Source analysis status: Analyzed
Weakness classifications: CWE-77
published: 2026-03-27T20:16:30.570
lastModified: 2026-11-11T23:10:00.263
The original JSON retains the logical configuration operators, exclusions and version bounds.
No normalized affected-package data is projected for this source revision. The original publisher record may contain additional product and version evidence; this does not establish that a package is unaffected.
Original source record · Cite this exact observation · Complete original publisher JSON
Go
SEMVER · introduced 0 → fixed 0.28.2
Original source record · Cite this exact observation · Complete original publisher JSON
Go
SEMVER · introduced 0 → fixed 0.28.2
Original source record · Cite this exact observation · Complete original publisher JSON