CVE-2021-21295: Possible request smuggling in HTTP/2 due missing validation
Noroxi assessment
Priority: Monitor (action score 29/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 18.8% (FIRST EPSS); higher than 97.3% of all records.
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
- According to CISA the attack is automatable: targets can be found by mass scanning.
- Fixed version: netty io.netty:netty-codec-http2 4.1.60.Final.
- Mentioned 2 times in Turkish national cyber security advisories (siberguvenlik.gov.tr).
Low priority for now. Upgrade to netty io.netty:netty-codec-http2 4.1.60.Final or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
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`.
- Published
- Mar 9, 2021
- Updated
- Oct 8, 2026
- EPSS
- 18.8% · 97th percentile
- CWE
- CWE-444
Report tools
Action score
29
Monitor
Low priority for now.
- CVSS
- 23 / 40 · 5.9 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 6 / 30 · 18.8%
CISA SSVC decision
- Exploitation
- none
- Automatable
- yes
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- 5.9
- CNA · GitHub_M
- 5.9
- agree
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| netty | netty | 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 | cpe:2.3:o:debian:debian_linux |
| quarkus | quarkus | cpe:2.3:a:quarkus:quarkus |
| apache | kudu | cpe:2.3:a:apache:kudu |
| apache | zookeeper | cpe:2.3:a:apache:zookeeper |
| oracle | communications cloud native core policy | cpe:2.3:a:oracle:communications_cloud_native_core_policy |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- apache kudubefore 1.16.0
- apache zookeeper3.5.9
- debian debian linux10.0
- netapp oncommand api servicesall versions
- netapp oncommand workflow automationall versions
- netty nettybefore 4.1.60
- oracle communications cloud native core policy1.14.0
- quarkus quarkusup to 1.13.7 inclusive
Versions reported by the vendor
Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.
netty io.netty:netty-codec-http2
- < 4.1.60.Finalaffected
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Debian:10 | netty | before 1:4.1.33-1+deb10u2 | 1:4.1.33-1+deb10u2 |
| Debian:12 | netty | before 1:4.1.48-3 | 1:4.1.48-3 |
| Maven | io.netty:netty | from 0 | — |
| Maven | io.netty:netty-codec-http2 | from 4.0.0 · before 4.1.60.Final | 4.1.60.Final |
| Maven | org.jboss.netty:netty | from 0 | — |
| openSUSE:Leap 15.2 | netty | before 4.1.13-lp152.3.3.1 | 4.1.13-lp152.3.3.1 |
| openSUSE:Leap 15.3 | netty | before 4.1.75-150200.4.6.2 | 4.1.75-150200.4.6.2 |
| openSUSE:Tumbleweed | netty | before 4.1.60-1.4 | 4.1.60-1.4 |
| Red Hat:a_mq_clients:2::el7 | python-qpid-proton | before 0:0.33.0-6.el7_9 | 0:0.33.0-6.el7_9 |
| Red Hat:a_mq_clients:2::el7 | python-qpid-proton-docs | before 0:0.33.0-6.el7_9 | 0:0.33.0-6.el7_9 |
| Red Hat:a_mq_clients:2::el7 | qpid-proton | before 0:0.33.0-6.el7_9 | 0:0.33.0-6.el7_9 |
| Red Hat:a_mq_clients:2::el7 | qpid-proton-c | before 0:0.33.0-6.el7_9 | 0:0.33.0-6.el7_9 |
| Red Hat:a_mq_clients:2::el7 | qpid-proton-c-devel | before 0:0.33.0-6.el7_9 | 0:0.33.0-6.el7_9 |
| Red Hat:a_mq_clients:2::el7 | qpid-proton-c-docs | before 0:0.33.0-6.el7_9 | 0:0.33.0-6.el7_9 |
| Red Hat:a_mq_clients:2::el7 | qpid-proton-cpp | before 0:0.33.0-6.el7_9 | 0:0.33.0-6.el7_9 |
| Red Hat:a_mq_clients:2::el7 | qpid-proton-cpp-devel | before 0:0.33.0-6.el7_9 | 0:0.33.0-6.el7_9 |
| Red Hat:a_mq_clients:2::el7 | qpid-proton-cpp-docs | before 0:0.33.0-6.el7_9 | 0:0.33.0-6.el7_9 |
| Red Hat:a_mq_clients:2::el7 | qpid-proton-debuginfo | before 0:0.33.0-6.el7_9 | 0:0.33.0-6.el7_9 |
| Red Hat:a_mq_clients:2::el7 | qpid-proton-tests | before 0:0.33.0-6.el7_9 | 0:0.33.0-6.el7_9 |
| Red Hat:a_mq_clients:2::el7 | rubygem-qpid_proton | before 0:0.33.0-6.el7_9 | 0:0.33.0-6.el7_9 |
| Red Hat:a_mq_clients:2::el8 | python-qpid-proton-docs | before 0:0.33.0-8.el8 | 0:0.33.0-8.el8 |
| Red Hat:a_mq_clients:2::el8 | python3-qpid-proton | before 0:0.33.0-8.el8 | 0:0.33.0-8.el8 |
| Red Hat:a_mq_clients:2::el8 | python3-qpid-proton-debuginfo | before 0:0.33.0-8.el8 | 0:0.33.0-8.el8 |
| Red Hat:a_mq_clients:2::el8 | qpid-proton | before 0:0.33.0-8.el8 | 0:0.33.0-8.el8 |
+96
Same product
netty: all recordsOther highest-scoring records for the same primary product.
- CVE-2026-47691Netty has Insufficient Bailiwick Validation for NS Records40Plan
- CVE-2026-45674Netty Vulnerable to DNS Cache Poisoning via Missing Bailiwick Checks in CNAME Records40Plan
- CVE-2019-20445HttpObjectDecoder.java in Netty before 4.1.44 allows a Content-Length header to be accompanied by a second Content-Length header, or by a Tr40Plan
Published before and after this one in the same product
- ← EarlierCVE-2020-11612Apr 7, 2020 · The ZlibDecoders in Netty 4.1.x before 4.1.46 allow for unbounded memory allocation while decoding a ZlibEncoded byte stream.33Monitor
- ← EarlierCVE-2021-21290Feb 8, 2021 · Local Information Disclosure Vulnerability in Netty on Unix-Like systems due temporary files23Monitor
- Later →CVE-2021-21409Mar 30, 2021 · Possible request smuggling in HTTP/2 due missing validation of content-length24Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| netty io.netty:netty-codec-http2 | 4.1.60.Final · description | Vendor (CNA) |
| debian:netty | 1:4.1.48-3 · Debian:12 | Package registry (OSV) |
| Maven:io.netty:netty-codec-http2 | 4.1.60.Final | Package registry (OSV) |
| opensuse:netty | 4.1.75-150200.4.6.2 · openSUSE:Leap 15.3 | Package registry (OSV) |
| red hat:python-qpid-proton | 0:0.33.0-6.el7_9 · Red Hat:a_mq_clients:2::el7 | Package registry (OSV) |
| red hat:python-qpid-proton-docs | 0:0.33.0-6.el7_9 · Red Hat:a_mq_clients:2::el7 | Package registry (OSV) |
| red hat:qpid-proton | 0:0.33.0-6.el7_9 · Red Hat:a_mq_clients:2::el7 | Package registry (OSV) |
| red hat:qpid-proton-c | 0:0.33.0-6.el7_9 · Red Hat:a_mq_clients:2::el7 | Package registry (OSV) |
| red hat:qpid-proton-c-devel | 0:0.33.0-6.el7_9 · Red Hat:a_mq_clients:2::el7 | Package registry (OSV) |
| red hat:qpid-proton-c-docs | 0:0.33.0-6.el7_9 · Red Hat:a_mq_clients:2::el7 | Package registry (OSV) |
| red hat:qpid-proton-cpp | 0:0.33.0-6.el7_9 · Red Hat:a_mq_clients:2::el7 | Package registry (OSV) |
| red hat:qpid-proton-cpp-devel | 0:0.33.0-6.el7_9 · Red Hat:a_mq_clients:2::el7 | Package registry (OSV) |
| red hat:qpid-proton-cpp-docs | 0:0.33.0-6.el7_9 · Red Hat:a_mq_clients:2::el7 | Package registry (OSV) |
| red hat:qpid-proton-debuginfo | 0:0.33.0-6.el7_9 · Red Hat:a_mq_clients:2::el7 | Package registry (OSV) |
| red hat:qpid-proton-tests | 0:0.33.0-6.el7_9 · Red Hat:a_mq_clients:2::el7 | Package registry (OSV) |
| red hat:rubygem-qpid_proton | 0:0.33.0-6.el7_9 · Red Hat:a_mq_clients:2::el7 | Package registry (OSV) |
| rocky linux:libdb | 0:5.3.28-42.el8_4 · Rocky Linux:8 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
No history yet (it accumulates with the daily EPSS job).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
National notice (Türkiye Cybersecurity Directorate / USOM)
Official security notices citing this record; remediation advice is on the agency's page.
- TR-21-0949 · Nov 25, 2021(IBM Güvenlik Bülteni Yayınladı)
- TR-21-0557 · Jul 7, 2021(IBM Güvenlik Bülteni Yayınladı)
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- none
- Integrity
- high · data or configuration can be modified
- Availability
- none
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- High
- Availability impact
- None
Weakness class (CWE)
CWE-444 · Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
ATT&CK techniques
—
Change log
- SSVC exploitation— → none
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (19 more)Show less
- github.com/netty/netty/commit/89c241e3b1795ff257af4ad6eadc616cb2fb3dc4
- github.com/netty/netty/security/advisories/GHSA-wm47-8v5p-wjpj
- lists.apache.org/thread.html/r02e467123d45006a1dda20a38349e9c74c3a4b53e2e07be0939ecb3f%40%3Cdev.ranger.apache.org%3E
- lists.apache.org/thread.html/r040a5e4d9cca2f98354b58a70b27099672276f66995c4e2e39545d0b%40%3Cissues.hbase.apache.org%3E
- lists.apache.org/thread.html/r04a3e0d9f53421fb946c60cc54762b7151dc692eb4e39970a7579052%40%3Ccommits.servicecomb.apache.org%3E
- lists.apache.org/thread.html/r0b09f3e31e004fe583f677f7afa46bd30110904576c13c5ac818ac2c%40%3Cissues.flink.apache.org%3E
- lists.apache.org/thread.html/r15f66ada9a5faf4bac69d9e7c4521cedfefa62df9509881603791969%40%3Cjira.kafka.apache.org%3E
- lists.apache.org/thread.html/r16c4b55ac82be72f28adad4f8061477e5f978199d5725691dcc82c24%40%3Ccommits.servicecomb.apache.org%3E
- lists.apache.org/thread.html/r1908a34b9cc7120e5c19968a116ddbcffea5e9deb76c2be4fa461904%40%3Cdev.zookeeper.apache.org%3E
- lists.apache.org/thread.html/r1bca0b81193b74a451fc6d687ab58ef3a1f5ec40f6c61561d8dd9509%40%3Cissues.zookeeper.apache.org%3E
- lists.apache.org/thread.html/r22adb45fe902aeafcd0a1c4db13984224a667676c323c66db3af38a1%40%3Ccommits.zookeeper.apache.org%3E
- lists.apache.org/thread.html/r22b2f34447d71c9a0ad9079b7860323d5584fb9b40eb42668c21eaf1%40%3Cissues.hbase.apache.org%3E
- lists.apache.org/thread.html/r268850f26639ebe249356ed6d8edb54ee8943be6f200f770784fb190%40%3Cissues.hbase.apache.org%3E
- lists.apache.org/thread.html/r27b7e5a588ec826b15f38c40be500c50073400019ce7b8adfd07fece%40%3Cissues.hbase.apache.org%3E
- lists.apache.org/thread.html/r2936730ef0a06e724b96539bc7eacfcd3628987c16b1b99c790e7b87%40%3Cissues.zookeeper.apache.org%3E
- lists.apache.org/thread.html/r2e93ce23e04c3f0a61e987d1111d0695cb668ac4ec4edbf237bd3e80%40%3Ccommits.servicecomb.apache.org%3E
- lists.apache.org/thread.html/r312ce5bd3c6bf08c138349b507b6f1c25fe9cf40b6f2b0014c9d12b1%40%3Cnotifications.zookeeper.apache.org%3E
- lists.apache.org/thread.html/r32b0b640ad2be3b858f0af51c68a7d5c5a66a462c8bbb93699825cd3%40%3Cissues.zookeeper.apache.org%3E
- lists.apache.org/thread.html/r33eb06b05afbc7df28d31055cae0cb3fd36cab808c884bf6d680bea5%40%3Cdev.zookeeper.apache.org%3E
Vendor advisories and official records. Exploit/PoC links are deliberately left out.