CVE-2024-45308

HedgeDoc is an open source, real-time, collaborative, markdown notes application. When using HedgeDoc 1 with MySQL or MariaDB, it is possible to create notes with an alias matching the ID of existing notes. The affected existing note can then not be accessed anymore and is effectively hidden by the new one. When the freeURL feature is enabled (by setting the allowFreeURL config option or the CMD_ALLOW_FREEURL environment variable to true), any user with the appropriate permissions can create a note with an arbitrary alias, e.g. by accessing it in the browser. When MySQL or MariaDB are used, it is possible to create a new note with an alias that matches the lower-cased ID of a different note. HedgeDoc then always presents the new note to users, as these databases perform case-insensitive matching and the lower-cased alias is found first. This issue only affects HedgeDoc instances that use MySQL or MariaDB. Depending on the permission settings of the HedgeDoc instance, the issue can be exploited only by logged-in users or by all (including non-logged-in) users. The exploit requires knowledge of the ID of the target note. Attackers could use this issue to present a manipulated copy of the original note to the user, e.g. by replacing the links with malicious ones. Attackers can also use this issue to prevent access to the original note, causing a denial of service. No data is lost, as the original content of the affected notes is still present in the database. Users are advised to upgrade to version 1.10.0 which addresses this issue. Users unable to upgrade may disable freeURL mode which prevents the exploitation of this issue. The impact can also be limited by restricting freeURL note creation to trusted, logged-in users by enabling requireFreeURLAuthentication/CMD_REQUIRE_FREEURL_AUTHENTICATION.

Weakness

The product receives an input value that is used as a resource identifier or other type of reference, but it does not validate or incorrectly validates that the input is equivalent to a potentially-unsafe value.

Extended Description

Attackers can sometimes bypass input validation schemes by finding inputs that appear to be safe, but will be dangerous when processed at a lower layer or by a downstream component. For example, a simple XSS protection mechanism might try to validate that an input has no “” tags using case-sensitive matching, but since HTML is case-insensitive when processed by web browsers, an attacker could inject “” and trigger XSS.

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

References

• https://github.com/hedgedoc/hedgedoc/commit/380587b7fd65bc1eb71eef51a3aab324f9877650
• https://github.com/hedgedoc/hedgedoc/security/advisories/GHSA-pjf2-269h-cx7p