Sebastiaan van Stijn
e4ad708faf
These releases include 15 security fixes following the security policy: - net/http: HTTP/2 server crash due to HPACK encoder race HTTP/2 servers could end up crashing due to inadvertently modifying its HPACK encoder concurrently. This happens because the server modifies the HPACK encoder from two goroutines without synchronization: one uses the encoder to encode a HEADERS frame as part of a response sent to a client and the other modifies the encoder's table size when handling a SETTINGS frame containing SETTINGS_HEADER_TABLE_SIZE that a client sends. A malicious client can repeatedly send a request while changing the header table size to crash the server. Fix this issue by not applying SETTINGS_HEADER_TABLE_SIZE immediately. Instead, buffer any SETTINGS_HEADER_TABLE_SIZE received, and only apply the new value prior to the next time the server writes a frame. Thanks to RyotaK (https://ryotak.net) of GMO Flatt Security Inc. for reporting this issue. This is CVE-2026-97032 and Go issue https://go.dev/issue/81867. - net/http: HTTP/2 server memory exhaustion due to Trailer headers When "Trailer" headers are sent by a client, the HTTP server internally uses the header values to populate the Request.Trailer map passed to the server handler. Because Request.Trailer is a map, each entry incurs memory overhead. For HTTP/2 servers, a malicious client can exploit this by sending a "Trailer" header that declares a large number of fields, causing the server to allocate a disproportionate amount of memory while bypassing Server.MaxHeaderValueCount and Server.MaxHeaderBytes limits. This exploit is not applicable for HTTP/1 servers, which do not support multiplexing a large number of requests over one TCP connection, and whose Server.MaxHeaderBytes are calculated differently. Server.MaxHeaderValueCount and Server.MaxHeaderBytes limits are now applied towards the trailer fields declared in "Trailer" headers. Thanks to RyotaK (https://ryotak.net) of GMO Flatt Security Inc. for reporting this issue. This is CVE-2026-78659 and Go issue https://go.dev/issue/81857. - crypto/tls: reject malformed ECH outer extension references Multiple ECH outer extension references are not permitted under RFC 9849; previously, a client could send a well-crafted packet that could trigger memory exhaustion in the server process by specifying multiple references. We now reject these as malformed and curb the memory amplification vector as a result. This is CVE-2026-97031 and Go issue https://go.dev/issue/81855. - cmd/go: checksum bypass for golang.org/fips140 Previously, a user operating inside of a malicious Go project that defines a bogus golang.org/fips140 and operates a malicious GOMODPROXY the user chooses to connect to can serve an arbitrary module in its place. We now unpack the trusted ziphash for the bundled golang.org/fips140 module and construct its entry in the GOMODCACHE such that it can be verified by the toolchain. This is CVE-2026-94444 and Go issue https://go.dev/issue/81833. - cmd/go: checksum database bypass for golang.org/toolchain Previously, a user operating inside of a malicious Go project that defines a bogus golang.org/toolchain go.sum entry and operates a malicious GOMODPROXY the user chooses to use can bypass the intended checksum. We now ensure that golang.org/toolchain always goes to the network for the canonical checksum. This is CVE-2026-94447 and Go issue https://go.dev/issue/81834. - html/template: reset context tracking on consecutive template expressions When a JavaScript template literal contains consecutive expressions, the context tracking state was not properly reset upon entering a new expression. We now ensure that template-literal expression entries correctly reset context variables so all subsequent regular expression literals are accurately recognized and escaped. This is CVE-2026-94448 and Go issue https://go.dev/issue/81821. - html/template: recognize yield as regexp preceder keyword A trusted template author may have previously written a valid template wherein the use of the yield keyword would not be correctly escaped. We now ensure that valid keyword uses are escaped and non-keyword uses are not escaped. This is CVE-2026-97030 and Go issue https://go.dev/issue/81823. - net/textproto, mime/multipart: memory limit bypass when parsing MIME headers Parsing a multipart form could bypass memory limits and read an arbitrarily long line into memory when the remaining limit at the start of a part was less than 400 bytes. Multipart form memory limits are now properly enforced in this situation. Thanks to Jakub Ciolek (https://ciolek.dev) for reporting this issue. This is CVE-2026-94440 and Go issue https://go.dev/issue/81741. - net/http: HTTP/1 client connection desynchronization after CONNECT rejection When http.Transport sends an HTTP/1 CONNECT request with a non-empty Request.Body, it writes the body directly to the connection without framing after the request headers. If the server rejects the CONNECT request with a non-2xx keep-alive response, Transport returns the connection to the idle pool. Because CONNECT requests do not have a request body, the server may interpret the trailing body bytes as a subsequent pipelined HTTP/1.1 request on the connection, leaving the pooled connection desynchronized and causing the next caller that reuses it to read the response to the injected request. In reverse proxies (including httputil.ReverseProxy) that forward CONNECT requests through a shared Transport, this can lead to cross-user response poisoning. The HTTP/1 transport now closes a connection after sending a CONNECT request, regardless of the response status. In addition, ReverseProxy now rejects incoming CONNECT requests with a 405 Method Not Allowed response. ReverseProxy has never handled CONNECT requests in a useful fashion (it does not convert the connection into a bidirectional tunnel), so we do not expect this change to negatively affect any current users. Thanks to Xclow3n (Rajat Raghav) for reporting this issue. This is CVE-2026-56866 and Go issue https://go.dev/issue/81740. - net/http: HTTP/1 server connection desynchronization after 2xx CONNECT response When an HTTP server handler sent a 2xx response to an HTTP/1 CONNECT request and returned without hijacking the connection, the server improperly continued to read and serve requests from the connection. Since a 2xx response to an HTTP/1 CONNECT converts the connection into a tunnel, the server should not treat the connection as continuing to contain HTTP. The impact of this misbehavior is mostly limited to potential request smuggling, where an intermediate proxy considers the data on the connection to be tunneled and the server considers it to be HTTP. The HTTP/1 server now always closes a connection after responding to a CONNECT request, regardless of the response status. Thanks to Jakub Ciolek (https://ciolek.dev) for reporting this issue. This is CVE-2026-94439 and Go issue https://go.dev/issue/81744. - net/http: excessive CPU consumption from repeated initial window changes A malicious HTTP/2 peer could cause excessive CPU consumption in the client or server by opening a large number of streams and then sending many small SETTINGS frames containing SETTINGS_INITIAL_WINDOW_SIZE values. The HTTP/2 client and server now efficiently handle changes to the initial window size (O(1) rather than O(number of streams)). Thanks to Jakub Ciolek (https://ciolek.dev) for reporting this issue. This is CVE-2026-78669 and Go issue https://go.dev/issue/81742. - net/http: HTTP/2 transport accepts malformed framing-related headers Historically, we have been rather lax about malformed framing-related headers in our HTTP/2 implementation, as they cannot interfere with HTTP/2 framing. However, this makes it possible for our HTTP/2 implementation to forward responses containing such headers to an HTTP/1 client when acting as a reverse proxy. If the HTTP/1 client also does not behave strictly enough, this can result in response smuggling. We now delete malformed framing-related headers when received by our HTTP/2 transport, so they will not be forwarded to a potentially vulnerable HTTP/1 client. Thanks to TJ Barton for reporting this issue. This is CVE-2026-78660 and Go issue https://go.dev/issue/81115. - os: Root.Mkdir(All) can follow junctions out of the root on Windows On Windows, when the target of Root.Mkdir or Root.MkdirAll was a junction pointing to an empty location, the operation would create a directory at the junction target even when that target was located outside the root. This only applies to operations where the last path component is a junction (path/to/junction, but not path/junction/target). Root.Mkdir and Root.MkdirAll now correctly avoid resolving junctions. Thanks to Daniele Ballarini for reporting this issue. This is CVE-2026-56857 and Go issue https://go.dev/issue/81739. - net/http: lack of limit on size of parsed Range headers When parsing a Range header containing a large number of small ranges, FileServer(FS), ServeContent, and ServeFile(FS) could consume an excessive amount of CPU. These functions now ignore Range headers containing more than 200 ranges. The limit is controlled by the new httpservecontentmaxranges= GODEBUG setting. Setting GODEBUG=httpservecontentmaxranges=0 disables the limit. Thanks to Jakub Ciolek (https://ciolek.dev) for reporting this issue. This is CVE-2026-78667 and Go issue https://go.dev/issue/81858. - net/http: double flow control refund on HTTP/2 server streams The HTTP/2 server could refund connection-level flow control twice for the same data: Once when a client resets a stream (refunding data for any sent-but-unread portion of the stream), and again when a request handler reads the buffered data. A malicious client could exploit this to bypass the configured connection-level flow control limit (MaxReceiveBufferPerConnection). Total buffered data is still limited by the concurrent stream limit and stream-level flow control. The HTTP/2 server now waits to refund connection-level flow control for reset streams until after the request handler is complete. Thanks to Ali Sherif (https://www.linkedin.com/in/ali-sherif-13812b276/) for reporting this issue. This is CVE-2026-78663 and Go issue https://go.dev/issue/81743. release notes: https://go.dev/doc/devel/release#go1.27.2 Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
containerd is an industry-standard container runtime with an emphasis on simplicity, robustness, and portability. It is available as a daemon for Linux and Windows, which can manage the complete container lifecycle of its host system: image transfer and storage, container execution and supervision, low-level storage and network attachments, etc.
containerd is a member of CNCF with 'graduated' status.
containerd is designed to be embedded into a larger system, rather than being used directly by developers or end-users.
Announcements
Now Recruiting
We are a large inclusive OSS project that is welcoming help of any kind shape or form:
- Documentation help is needed to make the product easier to consume and extend.
- We need OSS community outreach/organizing help to get the word out; manage and create messaging and educational content; and help with social media, community forums/groups, and google groups.
- We are actively inviting new security advisors to join the team.
- New subprojects are being created, core and non-core that could use additional development help.
- Each of the containerd projects has a list of issues currently being worked on or that need help resolving.
- If the issue has not already been assigned to someone or has not made recent progress, and you are interested, please inquire.
- If you are interested in starting with a smaller/beginner-level issue, look for issues with an
exp/beginnertag, for example containerd/containerd beginner issues.
Getting Started
See our documentation on containerd.io:
To get started contributing to containerd, see CONTRIBUTING.
If you are interested in trying out containerd see our example at Getting Started.
Nightly builds
There are nightly builds available for download here.
Binaries are generated from main branch every night for Linux and Windows.
Please be aware: nightly builds might have critical bugs, it's not recommended for use in production and no support provided.
Kubernetes (k8s) CI Dashboard Group
The k8s CI dashboard group for containerd contains test results regarding the health of kubernetes when run against main and a number of containerd release branches.
Runtime Requirements
Runtime requirements for containerd are very minimal. Most interactions with
the Linux and Windows container feature sets are handled via runc and/or
OS-specific libraries (e.g. hcsshim for Microsoft).
The current required version of runc is described in RUNC.md.
There are specific features used by containerd core code and snapshotters that will require a minimum kernel version on Linux. With the understood caveat of distro kernel versioning, a reasonable starting point for Linux is a minimum 4.x kernel version.
The overlay filesystem snapshotter, used by default, uses features that were finalized in the 4.x kernel series. If you choose to use btrfs, there may be more flexibility in kernel version (minimum recommended is 3.18), but will require the btrfs kernel module and btrfs tools to be installed on your Linux distribution.
To use Linux checkpoint and restore features, you will need criu installed on
your system. See more details in Checkpoint and Restore.
Build requirements for developers are listed in BUILDING.
Supported Registries
Any registry which is compliant with the OCI Distribution Specification is supported by containerd.
For configuring registries, see registry host configuration documentation
Features
For a detailed overview of containerd's core concepts and the features it supports, please refer to the FEATURES.MD document.
Releases and API Stability
Please see RELEASES.md for details on versioning and stability of containerd components.
Downloadable 64-bit Intel/AMD binaries of all official releases are available on our releases page. Binaries are published for additional platforms as well; see Platform Support for the full list of platforms and the level of support for each.
For other architectures and distribution support, you will find that many Linux distributions package their own containerd and provide it across several architectures, such as Canonical's Ubuntu packaging.
Enabling command auto-completion
Starting with containerd 1.4, the urfave client feature for auto-creation of bash and zsh
autocompletion data is enabled. To use the autocomplete feature in a bash shell for example, source
the autocomplete/ctr file in your .bashrc, or manually like:
$ source ./contrib/autocomplete/ctr
Distribution of ctr autocomplete for bash and zsh
For bash, copy the contrib/autocomplete/ctr script into
/etc/bash_completion.d/ and rename it to ctr. The zsh_autocomplete
file is also available and can be used similarly for zsh users.
Provide documentation to users to source this file into their shell if
you don't place the autocomplete file in a location where it is automatically
loaded for the user's shell environment.
CRI
cri is a containerd plugin implementation of the Kubernetes container runtime interface (CRI). With it, you are able to use containerd as the container runtime for a Kubernetes cluster.
CRI Status
cri is a native plugin of containerd. Since containerd 1.1, the cri plugin is built into the release binaries and enabled by default.
The cri plugin has reached GA status, representing that it is:
- Feature complete
- Works with Kubernetes 1.10 and above
- Passes all CRI validation tests.
- Passes all node e2e tests.
- Passes all e2e tests.
See results on the containerd k8s test dashboard
Validating Your cri Setup
A Kubernetes incubator project, cri-tools, includes programs for exercising CRI implementations. More importantly, cri-tools includes the program critest which is used for running CRI Validation Testing.
CRI Guides
- Installing with Ansible and Kubeadm
- For Non-Ansible Users, Performing a Custom Installation Using the Release Tarball and Kubeadm
- CRI Plugin Testing Guide
- Debugging Pods, Containers, and Images with
crictl - Configuring
criPlugins - Configuring containerd
Communication
For async communication and long-running discussions please use issues and pull requests on the GitHub repo. This will be the best place to discuss design and implementation.
For sync communication catch us in the #containerd and #containerd-dev Slack channels on Cloud Native Computing Foundation's (CNCF) Slack - cloud-native.slack.com. Everyone is welcome to join and chat. Get Invite to CNCF Slack.
Join our next community meeting hosted on Zoom. The schedule is posted on the CNCF Calendar (search 'containerd' to filter).
Security audit
Security audits for the containerd project are hosted on our website. Please see the security page at containerd.io for more information.
Reporting security issues
Please follow the instructions at containerd/project
Licenses
The containerd codebase is released under the Apache 2.0 license. The README.md file and files in the "docs" folder are licensed under the Creative Commons Attribution 4.0 International License. You may obtain a copy of the license, titled CC-BY-4.0, at http://creativecommons.org/licenses/by/4.0/.
Project details
containerd is the primary open source project within the broader containerd GitHub organization.
However, all projects within the repo have common maintainership, governance, and contributing
guidelines which are stored in a project repository commonly for all containerd projects.
Please find all these core project documents, including the:
information in our containerd/project repository.
Adoption
Interested to see who is using containerd? Are you using containerd in a project? Please add yourself via pull request to our ADOPTERS.md file.