CVE-2021-21259

CVE-2021-21259 is a high-severity vulnerability in Hedgedoc with a CVSS 3.x base score of 7.4. 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-79.

Key facts

Description

HedgeDoc is open source software which lets you create real-time collaborative markdown notes. In HedgeDoc before version 1.7.2, an attacker can inject arbitrary JavaScript into a HedgeDoc note, which is executed when the note is viewed in slide mode. Depending on the configuration of the instance, the attacker may not need authentication to create or edit notes. The problem is patched in HedgeDoc 1.7.2. As a workaround, disallow loading JavaScript from 3rd party sites using the `Content-Security-Policy` header. Note that this will break some embedded content.

Frequently asked questions

What is CVE-2021-21259?
HedgeDoc is open source software which lets you create real-time collaborative markdown notes. In HedgeDoc before version 1.7.2, an attacker can inject arbitrary JavaScript into a HedgeDoc note, which is executed when the note is viewed in slide mode. Depending on the configuration of the instance, the attacker may not need authentication to create or edit notes. The problem is patched in HedgeDoc 1.7.2. As a workaround, disallow loading JavaScript from 3rd party sites using the `Content-Security-Policy` header. Note that this will break some embedded content.
How severe is CVE-2021-21259?
CVE-2021-21259 has a CVSS 3.x base score of 7.4, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2021-21259 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (68th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-21259?
CVE-2021-21259 affects Hedgedoc. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-21259?
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-2021-21259 published?
CVE-2021-21259 was published on 2021-01-22 and last updated on 2026-06-17.

References

Affected products (1)

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