How severe is CVE-2021-42697?

CVE-2021-42697 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-42697?

CVE-2021-42697 affects the following packages: com.typesafe.akka:akka-http-core_2.13.0-RC3 (Maven), com.typesafe.akka:akka-http-core_2.13.0-RC2 (Maven), com.typesafe.akka:akka-http-core_2.13.0-M5 (Maven), com.typesafe.akka:aakka-http-core_2.13.0-M3 (Maven), com.typesafe.akka:akka-http-core_2.13 (Maven), com.typesafe.akka:akka-http-core_2.13 (Maven), com.typesafe.akka:akka-http-core_2.12 (Maven), com.typesafe.akka:akka-http-core_2.12 (Maven), and 1 more. Ecosystems affected: Maven.

How do I fix CVE-2021-42697?

A fix is available for CVE-2021-42697; check the affected-versions list above or the advisory for the patched release of com.typesafe.akka:akka-http-core_2.13.0-RC3, then make sure no transitive dependency still pins the vulnerable range.

How do I detect CVE-2021-42697 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for com.typesafe.akka:akka-http-core_2.13.0-RC3, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-42697 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2021-42697 actively exploited in the wild?

Yes. There are 2 known exploit references for CVE-2021-42697, including 1 documented proof-of-concept exploit on Exploit-DB and 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-42697?

CVE-2021-42697 has an EPSS (Exploit Prediction Scoring System) score of 36.1%, placing it in the 98th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score warrants monitoring and prompt remediation.

What type of vulnerability is CVE-2021-42697?

CVE-2021-42697 is classified as CWE-674 (CWE-674). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-42697 published, and has it been updated?

CVE-2021-42697 was published on November 2, 2021 and was last updated on October 24, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕

☕ Maven

Not in CISA KEV

HIGH severity

CVE-2021-42697 — akka-http-core_2.13.0-RC3

HIGHFix: akka/akka-http#3924

CVE-2021-42697 is a high-severity (CVSS 7.5) CWE-674 vulnerability in com.typesafe.akka:akka-http-core_2.13.0-RC3. 2 public exploit or proof-of-concept references are indexed, so weaponization risk is real. A fix is available for com.typesafe.akka:akka-http-core_2.13.0-RC3 — see the affected versions and patch details below.

Uncontrolled Recursion in Akka HTTP

Also known asGHSA-3hw2-h67c-wq66

Published

Nov 2, 2021

Updated

Oct 24, 2026

Affected

9 pkgs

Patched

5 / 9

Exploits

2 known

Exploitation data as of Nov 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

36.1%probability of exploitation in next 30 days

Moderate Risk0.00%

Lower risk than most CVEs98th percentile — riskier than 98% of all scored CVEsHighest risk

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

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

9 pkgs affected

☕com.typesafe.akka:akka-http-core_2.13.0-RC3☕com.typesafe.akka:akka-http-core_2.13.0-RC2☕com.typesafe.akka:akka-http-core_2.13.0-M5☕com.typesafe.akka:aakka-http-core_2.13.0-M3☕com.typesafe.akka:akka-http-core_2.13☕com.typesafe.akka:akka-http-core_2.13☕com.typesafe.akka:akka-http-core_2.12☕com.typesafe.akka:akka-http-core_2.12+1 more

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

Description

Akka HTTP 10.1.x before 10.1.15 and 10.2.x before 10.2.7 can encounter stack exhaustion while parsing HTTP headers, which allows a remote attacker to conduct a Denial of Service attack by sending a User-Agent header with deeply nested comments.

Affected Packages

9 total 5 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`com.typesafe.akka:akka-http-core_2.13.0-RC3`	≥ 10.1.0	No fix
☕Maven	`com.typesafe.akka:akka-http-core_2.13.0-RC2`	≥ 10.1.0	No fix
☕Maven	`com.typesafe.akka:akka-http-core_2.13.0-M5`	≥ 10.1.0	No fix
☕Maven	`com.typesafe.akka:aakka-http-core_2.13.0-M3`	≥ 10.1.0	No fix
☕Maven	`com.typesafe.akka:akka-http-core_2.13`	≥ 10.1.0&&< 10.1.15	10.1.15`com.typesafe.akka:akka-http-core_2.13:10.1.15`
☕Maven	`com.typesafe.akka:akka-http-core_2.13`	≥ 10.2.0-M1&&< 10.2.7	10.2.7`com.typesafe.akka:akka-http-core_2.13:10.2.7`

Affected Products

1 product · 2 configurations

Application

http serverakka

≥ 10.2.0 && < 10.2.7

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

EDB-50892remotemultiple

Akka HTTP 10.1.14 - Denial of Service

by cxosmo · May 11, 2022

Exploit-DB Source

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for com.typesafe.akka:akka-http-core_2.13.0-RC3, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
A fix is available for CVE-2021-42697; check the affected-versions list above or the advisory for the patched release of com.typesafe.akka:akka-http-core_2.13.0-RC3, then make sure no transitive dependency still pins the vulnerable range.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2021-42697 in your dependencies?

Find it across Maven, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

7.5/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWE Classification

CWE-674CWE-674

Weaponization

No Nuclei template or Metasploit module yet. 2 public proof-of-concept references are listed on this page.

OpenSSF Scorecard

Package health score

akka-http

7.0/10

Maintained10/10

Code-Review8/10

Branch-ProtectionN/A

Assessed Nov 9, 2026

Timeline

Disclosed

Nov 2, 2021

First exploit

May 11, 2022

Last updated

Oct 24, 2026

Identifiers

CVE-2021-42697

GHSA-3hw2-h67c-wq66

References

Advisoryakka.io · blog Advisoryakka.io · akka http 10.2.7 released Advisoryakka.io · akka http 10.1.15 released Advisorydoc.akka.io · 2021 CVE 2021 42697 stack overflow parsing user agent Advisorynvd.nist.gov · CVE 2021 42697 Webgithub.com Webakka.io · blog Packagegithub.com · akka http Evidencepacketstormsecurity.com · Akka HTTP 10.1.14 Denial Of Service

Related vulnerabilities

This CVE is high severity; 4 of 8 other CVEs with CWE-674 are rated as high or higher (top: high).

CVE-2026-119191CVE-2026-63475GHSA-2wrx-84qj-4pcgCVE-2026-119187CVE-2026-61847CVE-2026-116586CVE-2026-109413CVE-2026-114605Browse all CWE-674

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedOct 24, 2026

CVE-2021-42697 — akka-http-core_2.13.0-RC3

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2021-42697 in your dependencies?