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01 Record

CVE-2021-21409

Possible request smuggling in HTTP/2 due missing validation of content-length

MediumPUBLISHEDCNA: GitHub_M
CNA base score5.9 CVSS v3.xCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
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02 Description

Possible request smuggling in HTTP/2 due missing validation of content-length

03 Exploitation and scoring

Exploitation
Assessed, none found. CISA's assessment recorded neither public exploit code nor evidence of exploitation when it was made.
SSVC decision
  • ExploitationnoneCISA recorded no public exploit code and no evidence of exploitation.
  • AutomatableyesAn attacker can reliably automate reconnaissance through exploitation, so this scales.
  • Technical ImpactpartialSuccessful exploitation gives limited control of the vulnerable component.
CISA publishes the decision points, not a final SSVC decision. The decision also depends on mission and well-being impact, which is a property of your deployment rather than of the vulnerability.
EPSS probability
4.93% probability of exploitation activity in the next 30 days.
EPSS percentile
Equal to or higher than the score of 91.8% of scored records. A rank, not a probability.
NVD base score
5.9 (CVSS v3.x), scored by the NVD independently of the CNA.
NVD CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
NVD analysis status
Modified. NVD last modified this record on 2026-10-08.
Red Hat severity
Moderate. Red Hat's rating for its own products, not a CVSS rating.

Exploit-prediction scores from FIRST. Independent scoring and analysis status from the NVD. Vendor severity from Red Hat. Exploitation assessment and catalog membership from CISA.

04 Metadata

Published
2021-03-30 15:05Z5 YR AGO
Last updated
2026-10-08 21:13Z20 DAYS AGO
Reserved
2020-12-22
Assigning CNA
GitHub_M
Record state
PUBLISHED
Severity
Medium (CVSS 5.9)
CNA CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
Weaknesses
  • CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')Base
Data version
5.2
Document digest
b7beae41b64d7662dae1301ed776f53c873af69970d25df29e0402c2b8968440

05 Affected products

VendorProductVersionsPlatforms
nettynetty< 4.1.61.Final—

06 References

07 Fixed in

Debian 12

  • netty
    Fixed in 1:4.1.48-4

Source: Debian Security Tracker, the Debian security team. Received through OSV.dev. Reformatted by exploit.cc.

Debian 13

  • netty
    Fixed in 1:4.1.48-4

Source: Debian Security Tracker, the Debian security team. Received through OSV.dev. Reformatted by exploit.cc.

Debian 14

  • netty
    Fixed in 1:4.1.48-4

Source: Debian Security Tracker, the Debian security team. Received through OSV.dev. Reformatted by exploit.cc.

Ubuntu 22.04 LTS

  • netty
    Fixed in 1:4.1.48-4+deb11u1build0.22.04.1

Source: Ubuntu, Canonical Ltd. Licensed under CC BY-SA 4.0. Received through OSV.dev. Reformatted by exploit.cc.

Ubuntu Pro 14.04 LTS

  • netty
    No fix yet

Source: Ubuntu, Canonical Ltd. Licensed under CC BY-SA 4.0. Received through OSV.dev. Reformatted by exploit.cc.

Ubuntu Pro 16.04 LTS

  • netty
    Fixed in 1:4.0.34-1ubuntu0.1~esm1
    Available with Ubuntu Pro: https://ubuntu.com/pro

Source: Ubuntu, Canonical Ltd. Licensed under CC BY-SA 4.0. Received through OSV.dev. Reformatted by exploit.cc.

Ubuntu Pro 18.04 LTS

  • netty
    Fixed in 1:4.1.7-4ubuntu0.1+esm2
    Available with Ubuntu Pro: https://ubuntu.com/pro

Source: Ubuntu, Canonical Ltd. Licensed under CC BY-SA 4.0. Received through OSV.dev. Reformatted by exploit.cc.

Ubuntu Pro 20.04 LTS

  • netty
    Fixed in 1:4.1.45-1ubuntu0.1~esm1
    Available with Ubuntu Pro: https://ubuntu.com/pro

Source: Ubuntu, Canonical Ltd. Licensed under CC BY-SA 4.0. Received through OSV.dev. Reformatted by exploit.cc.

A release or ecosystem missing from this list has no record here. It may be unaffected or not covered by the source. Source notices and licences.