How severe is CVE-2023-26103?

CVE-2023-26103 has a CVSS 3.x base score of 5.3, rated medium 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 low.

Is CVE-2023-26103 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (65th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2023-26103?

CVE-2023-26103 affects Deno. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2023-26103?

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

When was CVE-2023-26103 published?

CVE-2023-26103 was published on 2023-02-25 and last updated on 2026-06-17.

CVE-2023-26103

CVE-2023-26103 is a medium-severity vulnerability in Deno with a CVSS 3.x base score of 5.3. 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-1333.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
EPSS exploit prediction: 1% (65th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-1333
Affected product: Deno
Published: 2023-02-25
Last modified: 2026-06-17

Description

Versions of the package deno before 1.31.0 are vulnerable to Regular Expression Denial of Service (ReDoS) due to the upgradeWebSocket function, which contains regexes in the form of /s*,s*/, used for splitting the Connection/Upgrade header. A specially crafted Connection/Upgrade header can be used to significantly slow down a web socket server.

Frequently asked questions

What is CVE-2023-26103?: Versions of the package deno before 1.31.0 are vulnerable to Regular Expression Denial of Service (ReDoS) due to the upgradeWebSocket function, which contains regexes in the form of /s*,s*/, used for splitting the Connection/Upgrade header. A specially crafted Connection/Upgrade header can be used to significantly slow down a web socket server.
How severe is CVE-2023-26103?: CVE-2023-26103 has a CVSS 3.x base score of 5.3, rated medium 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 low.
Is CVE-2023-26103 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (65th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2023-26103?: CVE-2023-26103 affects Deno. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2023-26103?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2023-26103 published?: CVE-2023-26103 was published on 2023-02-25 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:deno:deno:*:*:*:*:*:*:*:*

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