GHSA-wm47-8v5p-wjpj · Severity: medium · Ecosystem: maven — Possible request smuggling in HTTP/2 due missing validation
Netty is an open-source, asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients. In Netty (io.netty:netty-codec-http2) before version 4.1.60.Final there is a vulnerability that enables request smuggling. If a Content-Length header is present in the original HTTP/2 request, the field is not validated by `Http2MultiplexHandler` as it is propagated up. This is fine as long as the request is not proxied through as HTTP/1.1. If the request comes in as an HTTP/2 stream, gets converted into the HTTP/1.1 domain objects (`HttpRequest`, `HttpContent`, etc.) via `Http2StreamFrameToHttpObjectCodec `and then sent up to the child channel's pipeline and proxied through a remote peer as HTTP/1.1 this may result in request smuggling. In a proxy case, users may assume the content-length is validated somehow, which is not the case. If the request is forwarded to a backend channel that is a HTTP/1.1 connection, the Content-Length now has meaning and needs to be checked. An attacker can smuggle requests inside the body as it gets downgraded from HTTP/2 to HTTP/1.1. For an example attack refer to the linked GitHub Advisory. Users are only affected if all of this is true: `HTTP2MultiplexCodec` or `Http2FrameCodec` is used, `Http2StreamFrameToHttpObjectCodec` is used to convert to HTTP/1.1 objects, and these HTTP/1.1 objects are forwarded to another remote peer. This has been patched in 4.1.60.Final As a workaround, the user can do the validation by themselves by implementing a custom `ChannelInboundHandler` that is put in the `ChannelPipeline` behind `Http2StreamFrameToHttpObjectCodec`.
Conclusion & alert: CVE-2021-21295 is rated Moderate Risk (62.5/100): CVSS Medium severity, with high exploitation likelihood (EPSS 18.89%, 97th percentile). Core evidence: EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +18.28% over the last day, indicating growing attacker interest. Mandatory action: High exploitation likelihood—assess exposure and prioritize remediation.
Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.
EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).
| # | Date | Old EPSS score | New EPSS score | Delta (New - Old) |
|---|---|---|---|---|
| 1 | 2026-06-15 | 0.61% | 18.89% | +18.28% |
| 2 | 2026-06-07 | 0.39% | 0.61% | +0.22% |
| 3 | 2026-04-23 | — | 0.39% | — |
Full EPSS history (70 records total)
CVSS metrics for this CVE.
| Base score | Version | Severity | Vector | Exploitability | Impact | Score source |
|---|---|---|---|---|---|---|
| 5.9 | 3.1 | MEDIUM |
|
2.2 | 3.6 | [email protected] |
| 5.9 | 3.1 | MEDIUM |
|
2.2 | 3.6 | [email protected] |
| 2.6 | 2.0 | LOW |
|
4.9 | 2.9 | [email protected] |
GHSA-wm47-8v5p-wjpj · Severity: medium · Ecosystem: maven — Possible request smuggling in HTTP/2 due missing validation
| vendor | priority | summary | link |
|---|---|---|---|
debian
|
not yet assigned | CVE-2021-21295 not yet assigned priority: Debian including 1 source packages (netty), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. | https://security-tracker.debian.org/tracker/CVE-2021-21295 |
redhat
|
medium | — | https://access.redhat.com/security/cve/CVE-2021-21295 |
suse
|
medium | CVE-2021-21295 severity moderate: SUSE including 16 source package names (5.0.0-beta1.2.122:netty-4.1.75-150200.4.6.2, 5.1.0.6.40:netty-4.1.75-150200.4.6.2, …), 53 product×package rows across 31 product lines (Container suse/manager/5.0/x86_64/server, Container suse/multi-linux-manager/5.1/x86_64/server, … (31 product lines)): Fixed 36, Known Not Affected 17. | https://www.suse.com/security/cve/CVE-2021-21295/ |
ubuntu
|
medium | CVE-2021-21295 medium priority: Ubuntu including 1 source packages (netty), 16 status rows across 16 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): released 10, ignored 5, needs-triage 1. | https://ubuntu.com/security/CVE-2021-21295 |
| Vendor | Product | Version | Raw CPE |
|---|---|---|---|
| netty | netty | < 4.1.60 | cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* |
| netapp | oncommand_api_services | — | cpe:2.3:a:netapp:oncommand_api_services:-:*:*:*:*:*:*:* |
| netapp | oncommand_workflow_automation | — | cpe:2.3:a:netapp:oncommand_workflow_automation:-:*:*:*:*:*:*:* |
| debian | debian_linux | 10.0 | cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:* |
| quarkus | quarkus | <= 1.13.7 | cpe:2.3:a:quarkus:quarkus:*:*:*:*:*:*:*:* |
| apache | kudu | < 1.16.0 | cpe:2.3:a:apache:kudu:*:*:*:*:*:*:*:* |
| apache | zookeeper | 3.5.9 | cpe:2.3:a:apache:zookeeper:3.5.9:*:*:*:*:*:*:* |
| oracle | communications_cloud_native_core_policy | 1.14.0 | cpe:2.3:a:oracle:communications_cloud_native_core_policy:1.14.0:*:*:*:*:*:*:* |