CVE-2021-42697

Uncontrolled Recursion in Akka HTTP

7.5 HighPublic exploitFix available

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.

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None

What an attacker can affect

Confidentiality: None
Integrity: None
Availability: High

Exploit likelihood

36.1%Up 34.8 points since Nov 3, 2021

What each source reports

NVD Score used 7.5

Record: CVE-2021-42697
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 2.0: 5.0 MediumAV:N/AC:L/Au:N/C:N/I:N/A:P
Weakness: CWE-674
Updated: 2026-11-02

CVE List No score

Record: CVE-2021-42697
Updated: 2026-11-02

EUVDEUVD-2022-2193 No score

Record: EUVD-2022-2193
Updated: 2026-11-03

GitHub AdvisoriesGHSA-3hw2-h67c-wq66 7.5

Uncontrolled Recursion in Akka HTTP

Akka HTTP 10.1.x 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.

Record: GHSA-3hw2-h67c-wq66
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-674, CWE-787
Updated: 2026-11-02

OSV 7.5

Record: CVE-2021-42697
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVGHSA-3hw2-h67c-wq66 7.5

Uncontrolled Recursion in Akka HTTP

Record: GHSA-3hw2-h67c-wq66
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-674, CWE-787
Updated: 2026-11-02

Affected products

akka http server

Affected packages

Affected packages
Package	Affected	Fixed
`com.typesafe.akka:akka-http-core_2.13.0-RC3` Maven	10.1.0 up to 10.1.15	10.1.15
`com.typesafe.akka:akka-http-core_2.13.0-RC2` Maven	10.1.0 up to 10.1.15	10.1.15
`com.typesafe.akka:akka-http-core_2.13.0-M5` Maven	10.1.0 up to 10.1.15	10.1.15
`com.typesafe.akka:aakka-http-core_2.13.0-M3` Maven	10.1.0 up to 10.1.15	10.1.15
`com.typesafe.akka:akka-http-core_2.13` Maven	10.1.0 up to 10.1.15	10.1.15
`com.typesafe.akka:akka-http-core_2.13` Maven	10.2.0-M1 up to 10.2.7	10.2.7
`com.typesafe.akka:akka-http-core_2.12` Maven	10.1.0 up to 10.1.15	10.1.15
`com.typesafe.akka:akka-http-core_2.12` Maven	10.2.0-M1 up to 10.2.7	10.2.7
`com.typesafe.akka:akka-http-core_2.11` Maven	10.1.0 up to 10.1.15	10.1.15
`com.typesafe.akka:akka-http-core_2.13.0-RC3` Maven	10.1.0 and later, plus listed versions 10.1.8	None known

Show 8 moreShow less

Affected packages
Package	Affected	Fixed
`com.typesafe.akka:akka-http-core_2.13.0-RC2` Maven	10.1.0 and later, plus listed versions 10.1.8	None known
`com.typesafe.akka:akka-http-core_2.13.0-M5` Maven	10.1.0 and later, plus listed versions 10.1.710.1.8	None known
`com.typesafe.akka:aakka-http-core_2.13.0-M3` Maven	10.1.0 and later	None known
`com.typesafe.akka:akka-http-core_2.13` Maven	10.1.0 up to 10.1.15, plus listed versions 10.1.1010.1.1110.1.1210.1.1310.1.1410.1.810.1.9	10.1.15
`com.typesafe.akka:akka-http-core_2.13` Maven	10.2.0-M1 up to 10.2.7, plus listed versions 10.2.010.2.0-RC110.2.0-RC210.2.110.2.2 Show 6 moreShow less 10.2.310.2.410.2.510.2.5-M110.2.5-M210.2.6	10.2.7
`com.typesafe.akka:akka-http-core_2.12` Maven	10.1.0 up to 10.1.15, plus listed versions 10.1.110.1.1010.1.1110.1.1210.1.13 Show 9 moreShow less 10.1.1410.1.210.1.310.1.410.1.510.1.610.1.710.1.810.1.9	10.1.15
`com.typesafe.akka:akka-http-core_2.12` Maven	10.2.0-M1 up to 10.2.7, plus listed versions 10.2.010.2.0-RC110.2.0-RC210.2.110.2.2 Show 6 moreShow less 10.2.310.2.410.2.510.2.5-M110.2.5-M210.2.6	10.2.7
`com.typesafe.akka:akka-http-core_2.11` Maven	10.1.0 up to 10.1.15, plus listed versions 10.1.110.1.1010.1.1110.1.1210.1.13 Show 9 moreShow less 10.1.1410.1.210.1.310.1.410.1.510.1.610.1.710.1.810.1.9	10.1.15

Public exploits

Links only. Every CVE stores no exploit code.

Public exploits
Source	Link	Date
Exploit-DB	Akka HTTP 10.1.14 - Denial of Service	2022-05-11
PoC in GitHub	cxosmo/CVE-2021-42697	2022-04-24

History

History
Recorded	Changed	Sources
Nov 3, 2026	aliases	EUVD
Nov 2, 2026	first indexed	CVE List, Exploit-DB, GitHub Advisories, NVD, OSV, PoC in GitHub

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-42697 is a high vulnerability (CVSS 7.5) in Akka Http Server, published November 2, 2021. Public exploit code exists. EPSS puts the chance of exploitation in the next 30 days at 36.1%, the 98th percentile. Fixed in com.typesafe.akka:akka-http-core_2.13.0-RC3 10.1.15.