Description

Improper verification of cryptographic signature vulnerability in DigiDoc libdigidocpp, DigiDoc DigiDoc4, DigiDoc DigiDoc Android, and DigiDoc DigiDoc iOS. The vulnerability allows an attacker to create forged digital signatures that are displayed a valid by affected DigiDoc software.This issue affects libdigidocpp: from 4.0.0 before 4.5.0; DigiDoc4: from 4.6.0 before 4.11.0; DigiDoc Android: from 2.7.0 before 3.1.0; DigiDoc iOS: from 2.7.0 before 3.1.0.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.5",
  "pubDate": "2026-10-12T11:17:08.617Z",
  "pubdate": "2026-10-12T11:17:08.617Z",
  "executiveSummary": "This vulnerability involves an improper verification of cryptographic signatures within the libdigidocpp library and associated applications, including DigiDoc4, DigiDoc Android, and DigiDoc iOS.\nThe flaw allows an attacker to generate and inject forged digital signatures that the affected software incorrectly validates as authentic.\nThis constitutes a critical failure in the integrity verification process, potentially undermining the non-repudiation and authentication properties of documents processed by these systems.\nThe scope of impact extends across desktop and mobile implementations, affecting versions: libdigidocpp (4.0.0 through 4.4.x), DigiDoc4 (4.6.0 through 4.10.x), and DigiDoc Android/iOS (2.7.0 through 3.0.x).\nAn attacker capable of crafting a malicious signature can deceive the application into accepting fraudulent documents as legitimate, presenting significant risks to secure document workflows and legal digital transactions.",
  "technicalDetails": "The root cause of this vulnerability lies in the implementation of the signature verification logic within the libdigidocpp library. The library fails to perform exhaustive validation of the cryptographic signature structure or the associated X.509 certificate chain, leading to scenarios where a maliciously crafted signature is accepted as valid.\nThe exploitation process centers on bypassing signature validation checks. An attacker can construct a document containing a forged digital signature that satisfies the flawed verification algorithm within the affected software. When a user opens or validates a compromised file using the vulnerable library, the software fails to detect the cryptographic discrepancy, erroneously confirming the signature's validity to the user or the underlying application logic.\nThe vulnerability affects the core document processing component shared across all listed DigiDoc products. Because this component is responsible for parsing and verifying signatures according to standard protocols, the deficiency is inherited by the end-user applications (DigiDoc4, DigiDoc Android, and DigiDoc iOS).\nAttack flow: First, the attacker generates a document with a forged signature designed to trigger the specific verification oversight. Second, the attacker distributes this document to users of the vulnerable software. Third, when the victim utilizes the DigiDoc application to verify the signature, the application executes the flawed logic in libdigidocpp, which fails to identify the forgery. Finally, the application interface renders a status indicating the signature is valid, providing the attacker with a successful outcome.\nThis vulnerability does not require prior authentication or elevated privileges, as it is triggered by the standard act of verifying a document signature. The exposure is largely driven by the user's interaction with the document. Post-exploitation impact involves the successful delivery of forged digital documents that are treated as authentic by the system, potentially facilitating unauthorized actions, contract fraud, or document tampering that bypasses organizational security controls. There is no requirement for network interaction if the user is presented with a local document, making this a pervasive risk for any workflow relying on the integrity of DigiDoc signatures."
}