CVE-2021-42697Public exploitNetwork attack vector

Remote shutdown via recursive header comment parsing

Published Nov 2, 2021 · Updated Aug 4, 2024

Uncontrolled recursion in Akka HTTP 10.1.x before 10.1.15 and 10.2.x before 10.2.7 allows remote attackers to crash application servers. The modeled-header parser recursively processes arbitrarily nested comment elements in User-Agent headers without limiting nesting depth, exhausting the call stack. An unauthenticated network request to an exposed server triggers a fatal stack overflow and complete application shutdown.

CVSS severity7.5
High
EPSS probability36.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uncontrolled recursion in Akka HTTP 10.1.x before 10.1.15 and 10.2.x before 10.2.7 allows remote attackers to crash application servers. The modeled-header parser recursively processes arbitrarily nested comment elements in User-Agent headers without limiting nesting depth, exhausting the call stack. An unauthenticated network request to an exposed server triggers a fatal stack overflow and complete application shutdown.

The record

CVE
CVE-2021-42697
Published
Nov 2, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-674, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 2, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST National Vulnerability DatabaseAV:N/AC:L/Au:N/C:N/I:N/A:P
6.7AkkaCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:P/RL:O/RC:C

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-674Uncontrolled Recursion
T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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