How severe is CVE-2021-42697?

CVE-2021-42697 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-42697 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 36% (98th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-42697?

CVE-2021-42697 affects Akka Http Server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-42697?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-42697 published?

CVE-2021-42697 was published on 2021-11-02 and last updated on 2026-06-17.

CVE-2021-42697

CVE-2021-42697 is a high-severity vulnerability in Akka Http Server with a CVSS 3.x base score of 7.5. Its EPSS exploit-prediction score of 36% places it in the 98th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-674.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 36% (98th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-674
Affected product: Akka Http Server
Published: 2021-11-02
Last modified: 2026-06-17

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.

Frequently asked questions

What is 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.
How severe is CVE-2021-42697?: CVE-2021-42697 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-42697 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 36% (98th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-42697?: CVE-2021-42697 affects Akka Http Server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-42697?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-42697 published?: CVE-2021-42697 was published on 2021-11-02 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:akka:http_server:*:*:*:*:*:*:*:*

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