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Response snapshot Oct 29, 2026, 02:31 UTC

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VulnerabilityGHSA-2hw4-c9m4-f2fj

knative.dev/pkg admission webhooks allow unbounded request-body memory exhaustion

Built a Go PoC ([cmd/poc-c2/main.go](https://github.com/knative/pkg/blob/1ad5a1ce0ee7043081cb50fd1acc6d36a9126844/cmd/poc-c2/main.go)) that runs the exact 8-line vulnerable snippet from [webhook/admission.go:109-117](https://github.

At a glance

Exploited
Not known
Severity
Not scored yet
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: knative.dev/pkg: 0.0.0-20260531000007-52dbd5ece63f. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-2hw4-c9m4-f2fj (opens a new tab)

What happened

⚠️ Update (verification, 2026-05-19): C-2 confirmed end-to-end — 4.5× amplification observed (worse than the advisory's conservative 2× claim)

Built a Go PoC ([cmd/poc-c2/main.go](https://github.com/knative/pkg/blob/1ad5a1ce0ee7043081cb50fd1acc6d36a9126844/cmd/poc-c2/main.go)) that runs the exact 8-line vulnerable snippet from [webhook/admission.go:109-117](https://github.com/knative/pkg/blob/1ad5a1ce0ee7043081cb50fd1acc6d36a9126844/webhook/admission.go#L109-L117) verbatim under the same http.

HandlerFunc shape (the full production admissionHandler at :85 requires *Webhook + AdmissionController + an informer-synced channel + controller-runtime / client-go scaffolding — the bug is the missing http.MaxBytesReader, nothing else in the handler). Bound to 127.0.0.1:18098.

PoC client streamed 2 GiB of a bytes over a raw TCP socket. runtime.MemStats.HeapAlloc sampler:

Continue reading
baseline: HeapAlloc = 0.32 MiB
peak: HeapAlloc = 9 217.38 MiB = 9.00 GiB
ratio: 4.50× the body size

The advisory predicted ~2× from io.TeeReader doubling the body once in bodyBuffer. The observed 4.5× ratio comes from the interaction of two amplifiers: bytes.Buffer.ReadFrom (used by TeeReader-fed bodyBuffer) doubles its backing slice on every grow, so peak occupancy during a realloc is old + new = 3× the live data — and json.Decoder holds its own working buffer in parallel. The advisory's 2× floor is comfortably exceeded.

Downstream impact reminder: this library backs every Knative serving / eventing controller, every Tekton Triggers / Pipelines webhook, KEDA, Sigstore policy-controller, Kpack, and many more. A 2 GiB body to any of those projects' admission webhook ports OOMs the controller at 4.5× the body — i.e., even a 128 MiB request OOMs a 512 MiB-limited Pod.

---

Summary

knative.dev/pkg's admission webhook handler reads the incoming HTTP request body via json.NewDecoder(io.TeeReader(r.Body, &bodyBuffer)) with no http.MaxBytesReader wrapping the body. Because every consumer of knative.

dev/pkg/webhook inherits this handler (Knative serving / eventing, Tekton Pipelines, KEDA, Sigstore policy-controller, and others), a single oversized POST to any of those projects' admission webhook ports drives the controller pod into memory exhaustion and OOM-kill. Worse, the io.

TeeReader design keeps a verbatim copy of the body in bodyBuffer while the decoder also materializes the parsed struct — so the peak memory usage is roughly twice the body size.

This is the same shape as CVE-2026-24514 (ingress-nginx) and GHSA-9539-c3xr-w9vm (Kyverno admission body OOM) filed today against the same antipattern.

Affected versions

- knative.dev/pkg — main HEAD on github.com/knative/pkg (verified 2026-05-18 against [webhook/admission.go](https://github.com/knative/pkg/blob/1ad5a1ce0ee7043081cb50fd1acc6d36a9126844/webhook/admission.go) sha 1ad5a1ce0ee7043081cb50fd1acc6d36a9126844). - Every release that ships the current [webhook/admission.go](https://github.com/knative/pkg/blob/1ad5a1ce0ee7043081cb50fd1acc6d36a9126844/webhook/admission.go) handler.

Vulnerable code

[webhook/admission.go:109-117](https://github.com/knative/pkg/blob/1ad5a1ce0ee7043081cb50fd1acc6d36a9126844/webhook/admission.go#L109-L117):

review := admissionv1.AdmissionReview{}
var bodyBuffer bytes.Buffer
if err := json.NewDecoder(io.TeeReader(r.Body, &bodyBuffer)).Decode(&review); err != nil {
 http.Error(w, fmt.Sprintf("could not decode body: %v", err), http.StatusBadRequest)
 return
}

There is no http.MaxBytesReader around r.Body. The standard library's json.NewDecoder will read until EOF or the matching closing }. The io.TeeReader simultaneously copies every byte read from r.Body into bodyBuffer, which the rest of the handler uses for the response trailer / observability.

Downstream impact (the reason this matters)

knative.dev/pkg/webhook is the default admission-webhook scaffolding for the entire Knative + CNCF webhook ecosystem:

| Consumer | Repo | Webhook surface | |---|---|---| | Knative serving | knative/serving | resource validation / defaulting | | Knative eventing | knative/eventing | resource validation / defaulting | | Tekton Pipelines | tektoncd/pipeline | Pipeline / Task / TaskRun validation | | Tekton Triggers | tektoncd/triggers | EventListener / Trigger validation | | KEDA | kedacore/keda | ScaledObject / ScaledJob validation | | Sigstore policy-controller | sigstore/policy-controller | ClusterImagePolicy mutating + validating | | Kpack | buildpacks-community/kpack | Image / Builder validation | | ...

| | |

Every one of these consumers ships the same io.ReadAll-equivalent body read with no upper bound. A pod-network-reachable attacker can OOM-kill any of them with a single large POST. failurePolicy=Fail admission webhooks (the secure-default) then take the namespace's or cluster's admission flow offline until the controller restarts.

Impact

- Class: CWE-770 unbounded allocation. Reachable from any pod-network client. - Severity per consumer: depends on how each consumer configures failurePolicy. For projects with failurePolicy=Fail (e.g., Sigstore policy-controller's image-policy enforcement), the consequence is cluster-wide admission outage.

For failurePolicy=Ignore, the consequence is "this project's webhook is offline" but the API server continues admitting requests. - Severity: matches the broader CVE-2026-24514 / GHSA-9539-c3xr-w9vm. Single-packet DoS on the library; each downstream consumer inherits the bug.

Reproduction

The exact same PoC built against Kyverno's admission handler reproduces this:

import socket
total = 2 ', 8443))
s.sendall(b'POST / HTTP/1.1\r\nHost: x\r\nContent-Type: application/json\r\nContent-Length: %d\r\nConnection: close\r\n\r\n' % total)
chunk = b'a' * (1 > 20): s.sendall(chunk)

Observed against the Kyverno admission handle

Affected package ranges reported by GitHub: knative.dev/pkg: < 0.0.0-20260531000007-52dbd5ece63f

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-2hw4-c9m4-f2fj (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-2hw4-c9m4-f2fj, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 28). knative.dev/pkg admission webhooks allow unbounded request-body memory exhaustion. https://kevwire.com/record/GHSA-2hw4-c9m4-f2fj

MLA

"knative.dev/pkg admission webhooks allow unbounded request-body memory exhaustion." KEVWire, 28 Oct. 2026, kevwire.com/record/GHSA-2hw4-c9m4-f2fj.

Chicago

KEVWire. "knative.dev/pkg admission webhooks allow unbounded request-body memory exhaustion." Last modified October 28, 2026. https://kevwire.com/record/GHSA-2hw4-c9m4-f2fj.

Evidence summary (plain text)

knative.dev/pkg admission webhooks allow unbounded request-body memory exhaustion (Oct 28, 2026).
Built a Go PoC ([cmd/poc-c2/main.go](https://github.com/knative/pkg/blob/1ad5a1ce0ee7043081cb50fd1acc6d36a9126844/cmd/poc-c2/main.go)) that runs the exact 8-line vulnerable snippet from [webhook/admission.go:109-117](https://github.com/knative/pkg/blob/1ad5a1ce0ee7043081cb50fd1acc6d36a9126844/webhook/admission.go#L109-L117) verbatim under the same http.HandlerFunc shape (the full production admissionHandler at :85 requires *Webhook + AdmissionController + an informer-synced channel + controller-runtime / client-go scaffolding — the bug is the missing http.MaxBytesReader, nothing else in the…
Sources:
GitHub-reviewed advisory GHSA-2hw4-c9m4-f2fj: https://github.com/advisories/GHSA-2hw4-c9m4-f2fj
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: GHSA-2hw4-c9m4-f2fj.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 29, 2026, 02:00 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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