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Vulnerability record · CVE-2021-42697 · published 2 November 2021

CVE-2021-42697: Akka http server vulnerability

Akka · Http Server

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.

7.5 CVSS 3.1 High EPSS 36% · top 1.6% CWE-674 · CWE-674
7.5CVSS 3.1 base score, v2 5.0
36%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
10References, 2 tagged exploit
17 Jun 2026Last modified by NVD

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.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://packetstormsecurity.com/files/167018/Akka-HTTP-10.1.14-Denial-Of-Service.html ExploitThird Party AdvisoryVDB Entry
https://akka.io/blog/ Vendor Advisory
https://akka.io/blog/news/2021/11/02/akka-http-10.2.7-released Release NotesVendor Advisory
https://akka.io/blog/news/2021/11/22/akka-http-10.1.15-released Release NotesVendor Advisory
https://doc.akka.io/docs/akka-http/current/security/2021-CVE-2021-42697-stack-overflow-parsing-user-agent.html Vendor Advisory
http://packetstormsecurity.com/files/167018/Akka-HTTP-10.1.14-Denial-Of-Service.html ExploitThird Party AdvisoryVDB Entry
https://akka.io/blog/ Vendor Advisory
https://akka.io/blog/news/2021/11/02/akka-http-10.2.7-released Release NotesVendor Advisory
https://akka.io/blog/news/2021/11/22/akka-http-10.1.15-released Release NotesVendor Advisory
https://doc.akka.io/docs/akka-http/current/security/2021-CVE-2021-42697-stack-overflow-parsing-user-agent.html Vendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

7.5CVE-2023-44487HTTP/2 Rapid Reset stream cancellation denial of serviceThe HTTP/2 protocol permits a client to cancel many streams quickly, and the server's handling of those resets consumes disproportionate resources. T…KEVEPSS 100%analysed7.5CVE-2017-1000118Akka http server memory buffer overflow vulnerabilityAkka HTTP versions <= 10.0.5 Illegal Media Range in Accept Header Causes StackOverflowError Leading to Denial of ServiceEPSS 1.1%

Source: NIST National Vulnerability Database (record CVE-2021-42697), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.