`CVE-2021-42697`

Severity	7.5 High CVSS 3.1 2 scores
Fixed in	`10.1.15`, `10.2.7`
Weakness	Out-of-bounds write (CWE-787)
Published	2 Nov 2021
Updated	17 Jun 2026

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.

CWE-674

Exploitation status

Working exploit published

A reviewed exploit catalogue lists ready-to-run exploit code for this CVE.

CISA KEV not listed
VulnCheck KEV not listed
CISA Vulnrichment no assessment published
Indexed PoC 2 indexed Published artifacts you can open, in Exploit-DB, GitHub PoC; first seen 2022-04-24.
EPSS 36% chance in 30 days A model's forecast, not a report of exploitation. Higher than 98% of all scored CVEs.

1 of these are GitHub repositories with fewer than 5 stars. They are listed for reference and don't count toward the exploitation status above.

Index	Artifact	Stars	First seen
GitHub PoC	Proof of concept exploit for CVE-2021-42697: 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.	1	2022-04-24
Exploit-DB	Akka HTTP 10.1.14 - Denial of Service		2022-05-11

Waratek protection

Mitigation candidate

A kind of vulnerability Waratek's rules address, with exploit code published or exploitation reported. No rule exists and none is planned yet. The decision below says what we found to build a rule from.

Protection none
Action unverified
Review automated Inferred
Record active

Decided by	The affected package being open source on Maven, so the fix can be read
Finding	This CVE affects an open-source Java library published on Maven Central (Maven packages: 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_2.12, com.typesafe.akka:akka-http-core_2.11), so it is squarely in ARMR's territory and the source needed to understand the defect is public. That makes it a candidate for an ARMR patch rule. No rule exists and none is scheduled: the diff between the affected and fixed versions has not been read, and a closer look may find no hook point ARMR can act on.

Decided by

The affected package being open source on Maven, so the fix can be read

Finding

This CVE affects an open-source Java library published on Maven Central (Maven packages: 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_2.12, com.typesafe.akka:akka-http-core_2.11), so it is squarely in ARMR's territory and the source needed to understand the defect is public. That makes it a candidate for an ARMR patch rule. No rule exists and none is scheduled: the diff between the affected and fixed versions has not been read, and a closer look may find no hook point ARMR can act on.

CVSS

7.5 HIGH v3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H 2 metrics

We show the highest score from the newest CVSS version. Scores from different versions can't be compared, and the first score listed is sometimes a 0.0 placeholder.

Version Score Band Vector Assigner Type

CVSS 3.1 7.5 HIGH CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H NVD Primary published

CVSS 2.0 5.0 none AV:N/AC:L/Au:N/C:N/I:N/A:P NVD Primary

Version	Score	Band	Vector	Assigner	Type
CVSS 3.1	7.5	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`	NVD	Primary	published
CVSS 2.0	5.0	none	`AV:N/AC:L/Au:N/C:N/I:N/A:P`	NVD	Primary

Affected software and releases

Maven packages

Affected and fixed versions, from OSV.dev

Package Introduced Fixed Last affected

com.typesafe.akka:akka-http-core_2.13.0-RC3 10.1.0 none unbounded

com.typesafe.akka:akka-http-core_2.13.0-RC2 10.1.0 none unbounded

com.typesafe.akka:akka-http-core_2.13.0-M5 10.1.0 none unbounded

com.typesafe.akka:aakka-http-core_2.13.0-M3 10.1.0 none unbounded

com.typesafe.akka:akka-http-core_2.13 10.1.0 10.1.15 unbounded

com.typesafe.akka:akka-http-core_2.13 10.2.0-M1 10.2.7 unbounded

com.typesafe.akka:akka-http-core_2.12 10.1.0 10.1.15 unbounded

com.typesafe.akka:akka-http-core_2.12 10.2.0-M1 10.2.7 unbounded

com.typesafe.akka:akka-http-core_2.11 10.1.0 10.1.15 unbounded

Package	Introduced	Fixed	Last affected
`com.typesafe.akka:akka-http-core_2.13.0-RC3`	10.1.0	none	unbounded
`com.typesafe.akka:akka-http-core_2.13.0-RC2`	10.1.0	none	unbounded
`com.typesafe.akka:akka-http-core_2.13.0-M5`	10.1.0	none	unbounded
`com.typesafe.akka:aakka-http-core_2.13.0-M3`	10.1.0	none	unbounded
`com.typesafe.akka:akka-http-core_2.13`	10.1.0	`10.1.15`	unbounded
`com.typesafe.akka:akka-http-core_2.13`	10.2.0-M1	`10.2.7`	unbounded
`com.typesafe.akka:akka-http-core_2.12`	10.1.0	`10.1.15`	unbounded
`com.typesafe.akka:akka-http-core_2.12`	10.2.0-M1	`10.2.7`	unbounded
`com.typesafe.akka:akka-http-core_2.11`	10.1.0	`10.1.15`	unbounded

Products and versions

8 products, 11 version entries

Source	Vendor	Product	Scheme	Affected versions
nvd	akka	http server	generic	≥ 10.1.0 and ＜ 10.1.15 · ≥ 10.2.0 and ＜ 10.2.7
osv	com.typesafe.akka	aakka-http-core_2.13.0-M3	generic	≥ 10.1.0
osv	com.typesafe.akka	akka-http-core_2.11	generic	≥ 10.1.0 and ＜ 10.1.15
osv	com.typesafe.akka	akka-http-core_2.12	generic	≥ 10.1.0 and ＜ 10.1.15 · ≥ 10.2.0 and ＜ 10.2.7
osv	com.typesafe.akka	akka-http-core_2.13	generic	≥ 10.1.0 and ＜ 10.1.15 · ≥ 10.2.0 and ＜ 10.2.7
osv	com.typesafe.akka	akka-http-core_2.13.0-M5	generic	≥ 10.1.0
osv	com.typesafe.akka	akka-http-core_2.13.0-RC2	generic	≥ 10.1.0
osv	com.typesafe.akka	akka-http-core_2.13.0-RC3	generic	≥ 10.1.0

Source

Vendor

Product

Scheme

Affected versions

nvd

akka

http server

generic

≥ 10.1.0 and ＜ 10.1.15 · ≥ 10.2.0 and ＜ 10.2.7

osv

com.typesafe.akka

aakka-http-core_2.13.0-M3

generic

≥ 10.1.0

osv

com.typesafe.akka

akka-http-core_2.11

generic

≥ 10.1.0 and ＜ 10.1.15

osv

com.typesafe.akka

akka-http-core_2.12

generic

≥ 10.1.0 and ＜ 10.1.15 · ≥ 10.2.0 and ＜ 10.2.7

osv

com.typesafe.akka

akka-http-core_2.13

generic

≥ 10.1.0 and ＜ 10.1.15 · ≥ 10.2.0 and ＜ 10.2.7

osv

com.typesafe.akka

akka-http-core_2.13.0-M5

generic

≥ 10.1.0

osv

com.typesafe.akka

akka-http-core_2.13.0-RC2

generic

≥ 10.1.0

osv

com.typesafe.akka

akka-http-core_2.13.0-RC3

generic

≥ 10.1.0

References

URL	Tags
https://github.com/akka/akka-http/pull/3924	WEB
https://akka.io/blog	WEB
https://akka.io/blog/news/2021/11/02/akka-http-10.2.7-released	WEB
https://akka.io/blog/news/2021/11/22/akka-http-10.1.15-released	WEB
https://doc.akka.io/docs/akka-http/current/security/2021-CVE-2021-42697-stack-overflow-parsing-user-agent.html	WEB
https://github.com/akka/akka-http	PACKAGE
http://packetstormsecurity.com/files/167018/Akka-HTTP-10.1.14-Denial-Of-Service.html	WEB
https://akka.io/blog/	Vendor Advisory

URL

Timeline

Published	2021-11-02	By the CVE Program.
NVD record modified	2026-06-17	NVD's own last-modified date for this record.

Published

2021-11-02

By the CVE Program.

NVD record modified

2026-06-17

NVD's own last-modified date for this record.

How VRT decided (17 of 24 rules ran)

17 of 24 rules ran. The rest didn't run because an earlier rule had already settled the CVE.

# Rule Outcome Status Detail

identity: Does this identifier describe a vulnerability at all? the first rule that matches decides

1 rejected no match CVE Program withdrawal of this identifier

scope: Is it a vulnerability Waratek protects? the first rule that matches decides

2 armr-patch-file no match An ARMR patch file on disk for this CVE

3 armr-secure-rule-file no match An ARMR security-rule template on disk for this CVE

4 manual-classification no match A researcher's recorded decision for this specific CVE

5 manual classification no match Manual classification of this CVE in the legacy dataset

6 non-java-upstream no match A root cause in non-Java code: an OS kernel, a C library, or a bundled runtime

7 oracle-component no match The defect being in a component of a tracked product the agent does not reach: JavaFX, the Java SE installer, the JInitiator browser plug-in, the native WebLogic proxy plug-in, or a native part of Oracle Application Server or Collaboration Suite (HTTP Server, Web Cache, Internet Directory, mail and calendar servers). Oracle gives these no CPE of their own and names them only in the description.

8 java-client-side no match Oracle's own risk-matrix note saying the CVE is reached only through untrusted code in the Java sandbox (applets, Web Start) or only through a client installation of Java, so a server running its own trusted code is not exposed

9 osv-maven matched In scope Maven packages: 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_2.12, com.typesafe.akka:akka-http-core_2.11

10 cna-maven-package not reached An affected Maven artifact named by the CNA itself

11 known-cpe-product not reached An NVD CPE naming a product ARMR tracks

12 cna-cpe-product not reached A CPE the CNA published naming a tracked product. Oracle publishes these on advisory day, months before NVD.

13 oracle-advisory-family not reached A tracked product family named in Oracle's own risk matrix. CPE cannot carry a suite name, only a module.

14 cna-named-product not reached A tracked product named in words by the CVE's own CNA, on a record with no CPE yet. Apache and Eclipse publish these on advisory day, before NVD adds CPE data.

15 non-deployable-product not reached The only affected product being a sealed appliance image, where Java runs but no -javaagent can be attached

16 unmatched-product not reached No tracked product matched above, and none present at all

disposition: What do we do about one that is? every rule runs

17 patch-hint no match A reference pointing at the upstream fix: a commit, a PR, a Red Hat bug

18 open-source-maven decided it matched Mitigation candidate Open-source Maven artifact indexed by OSV (Maven packages: 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_2.12, com.typesafe.akka:akka-http-core_2.11). The source is public, which makes an ARMR patch rule a candidate; nothing here establishes that one can be written.

19 poc-derivable skipped An indexed exploit clearing the evidence bar to reverse-engineer, where there is no source to read

20 no-exploit skipped Nothing to build a rule from yet: no published exploit, no CISA record of exploitation and no source-level change to read

21 secure-rule-match no match A vulnerability class already blocked by an ARMR security rule

22 exploited-no-fix-or-poc skipped Somebody exploiting this CVE (a CISA or VulnCheck KEV listing, or a CISA verdict of active exploitation), with no fix, source code or PoC to build a rule from

23 below-action-threshold no match Severity is HIGH — only MEDIUM/LOW are deprioritized

24 no-exploit-published no match A CISA or VulnCheck KEV listing, a CISA verdict of active exploitation, a reviewed exploit catalogue, or a GitHub PoC with 5 or more stars carries this CVE — exploit code is in use or published, so it stays a candidate

Products the scope rules checked

The products this CVE's record names, and whether VRT tracks each one. The scope rules decided on these.

Vendor Product Tracked CPE Source

akka http_server not tracked cpe:2.3:a:akka:http_server:*:*:*:*:*:*:*:*

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