How severe is CVE-2023-50247?

CVE-2023-50247 has a CVSS 3.x base score of 3.7, rated low severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.

Is CVE-2023-50247 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2023-50247?

CVE-2023-50247 primarily affects Dena H2o. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2023-50247?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2023-50247 published?

CVE-2023-50247 was published on 2023-12-12 and last updated on 2026-06-17.

CVE-2023-50247

CVE-2023-50247 is a low-severity vulnerability in Dena H2o with a CVSS 3.x base score of 3.7. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-770.

Key facts

Severity: Low (CVSS 3.x base score 3.7)
EPSS exploit prediction: 1% (54th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-770
Affected product: Dena H2o
Published: 2023-12-12
Last modified: 2026-06-17

Description

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. The QUIC stack (quicly), as used by H2O up to commit 43f86e5 (in version 2.3.0-beta and prior), is susceptible to a state exhaustion attack. When H2O is serving HTTP/3, a remote attacker can exploit this vulnerability to progressively increase the memory retained by the QUIC stack. This can eventually cause H2O to abort due to memory exhaustion. The vulnerability has been resolved in commit d67e81d03be12a9d53dc8271af6530f40164cd35. HTTP/1 and HTTP/2 are not affected by this vulnerability as they do not use QUIC. Administrators looking to mitigate this issue without upgrading can disable HTTP/3 support.

Frequently asked questions

What is CVE-2023-50247?: h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. The QUIC stack (quicly), as used by H2O up to commit 43f86e5 (in version 2.3.0-beta and prior), is susceptible to a state exhaustion attack. When H2O is serving HTTP/3, a remote attacker can exploit this vulnerability to progressively increase the memory retained by the QUIC stack. This can eventually cause H2O to abort due to memory exhaustion. The vulnerability has been resolved in commit d67e81d03be12a9d53dc8271af6530f40164cd35. HTTP/1 and HTTP/2 are not affected by this vulnerability as they do not use QUIC. Administrators looking to mitigate this issue without upgrading can disable HTTP/3 support.
How severe is CVE-2023-50247?: CVE-2023-50247 has a CVSS 3.x base score of 3.7, rated low severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.
Is CVE-2023-50247 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2023-50247?: CVE-2023-50247 primarily affects Dena H2o. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2023-50247?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2023-50247 published?: CVE-2023-50247 was published on 2023-12-12 and last updated on 2026-06-17.

References

Affected products (3)

cpe:2.3:a:dena:h2o:*:*:*:*:*:*:*:*
cpe:2.3:a:dena:h2o:2.3.0:beta1:*:*:*:*:*:*
cpe:2.3:a:dena:h2o:2.3.0:beta2:*:*:*:*:*:*

More vulnerabilities in Dena H2o

CVE-2018-0608 — Critical (CVSS 9.8): Buffer overflow in H2O version 2.2.4 and earlier allows remote attackers to execute arbitrary code or cause a denial of…
CVE-2016-7835 — Critical (CVSS 9.1): Use-after-free vulnerability in H2O allows remote attackers to cause a denial-of-service (DoS) or obtain server…
CVE-2023-30847 — High (CVSS 8.2): H2O is an HTTP server. In versions 2.3.0-beta2 and prior, when the reverse proxy handler tries to processes a certain…
CVE-2023-44487 — High (CVSS 7.5): The HTTP/2 protocol allows a denial of service (server resource consumption) because request cancellation can reset…
CVE-2017-10908 — High (CVSS 7.5): H2O version 2.2.3 and earlier allows remote attackers to cause a denial of service in the server via specially crafted…
CVE-2017-10869 — High (CVSS 7.5): Buffer overflow in H2O version 2.2.2 and earlier allows remote attackers to cause a denial-of-service in the server via…

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