How severe is CVE-2021-25761?

CVE-2021-25761 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 low, integrity none, and availability none.

Is CVE-2021-25761 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (42nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-25761?

CVE-2021-25761 affects Jetbrains Ktor. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-25761?

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

When was CVE-2021-25761 published?

CVE-2021-25761 was published on 2021-02-03 and last updated on 2026-06-17.

CVE-2021-25761

CVE-2021-25761 is a medium-severity vulnerability in Jetbrains Ktor 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-326.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
CVSS v2: 5.0
EPSS exploit prediction: 1% (42nd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-326
Affected product: Jetbrains Ktor
Published: 2021-02-03
Last modified: 2026-06-17

Description

In JetBrains Ktor before 1.5.0, a birthday attack on SessionStorage key was possible.

Frequently asked questions

What is CVE-2021-25761?: In JetBrains Ktor before 1.5.0, a birthday attack on SessionStorage key was possible.
How severe is CVE-2021-25761?: CVE-2021-25761 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 low, integrity none, and availability none.
Is CVE-2021-25761 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (42nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-25761?: CVE-2021-25761 affects Jetbrains Ktor. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-25761?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-25761 published?: CVE-2021-25761 was published on 2021-02-03 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:jetbrains:ktor:*:*:*:*:*:*:*:*

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