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MEDIUM severity

CVE-2021-42009 — trafficcontrol

MEDIUM

CVE-2021-42009 is a medium-severity (CVSS 4.3) Improper Input Validation vulnerability in github.com/apache/trafficcontrol. A fix is available for github.com/apache/trafficcontrol — see the affected versions and patch details below.

Email relay in Apache Traffic Control

Also known asGHSA-gw97-f6h8-gm94GO-2022-0602
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 11, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
2.8%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs86th percentile — riskier than 86% of all scored CVEsHighest risk
0.00%1.16%2.32%3.48%0.7%2.8%Apr 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-42009 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,987 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected
🐹github.com/apache/trafficcontrol

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

An authenticated Apache Traffic Control Traffic Ops user with Portal-level privileges can send a request with a specially-crafted email subject to the /deliveryservices/request Traffic Ops endpoint to send an email, from the Traffic Ops server, with an arbitrary body to an arbitrary email address. Apache Traffic Control 5.1.x users should upgrade to 5.1.3 or 6.0.0. 4.1.x users should upgrade to 5.1.3.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/apache/trafficcontrolall versions5.1.3go get github.com/apache/trafficcontrol@v5.1.3

Affected Products

1 product · 1 configurations
Application
traffic controlapache
≥ 4.1.0 && < 5.1.3
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/apache/trafficcontrol, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update github.com/apache/trafficcontrol to 5.1.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-42009 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

An authenticated Apache Traffic Control Traffic Ops user with Portal-level privileges can send a request with a specially-crafted email subject to the /deliveryservices/request Traffic Ops endpoint to send an email, from the Traffic Ops server, with an arbitrary body to an arbitrary email address. Apache Traffic Control 5.1.x users should upgrade to 5.1.3 or 6.0.0. 4.1.x users should upgrade to 5.1.3.
O3 Security · Impact-Aware SCA

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CVE-2021-42009: trafficcontrol — Fixed in 5.1.3