CVE-2026-59112 Overview
CVE-2026-59112 is a signature verification vulnerability affecting the Estonian Information System Authority (RIA) DigiDoc ecosystem. The flaw exists in libdigidocpp, DigiDoc4, and the DigiDoc mobile clients for Android and iOS. It combines improper verification of a cryptographic signature [CWE-347] with an improper check for unusual or exceptional conditions. An attacker with local access and user interaction can present a document whose signature integrity is not properly enforced. The issue affects libdigidocpp 4.1.0 through versions prior to 4.2.1, DigiDoc4 4.7.0 through versions prior to 4.8.2, DigiDoc on Android 2.7.0 through versions prior to 2.7.2, and DigiDoc on iOS 2.8.0 through versions prior to 2.8.1.
Critical Impact
An attacker can undermine the integrity guarantees of signed documents processed by DigiDoc, which are used for legally binding electronic signatures in Estonia.
Affected Products
- libdigidocpp from 4.1.0 before 4.2.1
- DigiDoc4 from 4.7.0 before 4.8.2
- DigiDoc on Android from 2.7.0 before 2.7.2 and DigiDoc on iOS from 2.8.0 before 2.8.1
Discovery Timeline
- 2026-08-10 - CVE-2026-59112 published to the National Vulnerability Database
- 2026-08-10 - Last updated in NVD database
Technical Details for CVE-2026-59112
Vulnerability Analysis
The vulnerability resides in how the DigiDoc client stack validates cryptographic signatures on ASiC-E and BDOC containers. Signature verification fails to properly enforce integrity checks under specific conditions, and the code does not correctly handle exceptional conditions encountered while parsing signed content. The result is that a container may be treated as validly signed even when the cryptographic binding between signer, signature, and payload is not fully proven. Because DigiDoc is the reference client for Estonian eID signatures, this affects the trust semantics of documents used for contracts, government filings, and other legal transactions. Refer to the RIA Blog Security Vulnerability Analysis for the vendor's technical writeup.
Root Cause
The root cause is improper verification of a cryptographic signature combined with missing handling of exceptional parsing states, as classified under [CWE-347]. The fix in libdigidocpp tightens validation logic so that signatures failing structural or cryptographic checks are rejected rather than silently accepted. See GitHub Pull Request #690 for the source-level change.
Attack Vector
The attack vector is local and requires user interaction. An attacker must deliver a specially crafted DigiDoc container to a target user, who then opens or verifies the container inside an affected DigiDoc client. Successful exploitation can cause the client to display a manipulated document as validly signed, damaging the integrity assurances of the signature workflow. No confidentiality or availability impact is expected; the effect is on integrity of signature validation results.
No public exploit code is available for CVE-2026-59112. See the GitHub Pull Request #690 for the corrective patch details.
Detection Methods for CVE-2026-59112
Indicators of Compromise
- Presence of DigiDoc containers (.asice, .bdoc, .ddoc) received from untrusted senders that trigger validation warnings in patched clients.
- Installations of libdigidocpp, DigiDoc4, or mobile DigiDoc clients running versions below the fixed releases.
Detection Strategies
- Inventory endpoints and mobile devices for DigiDoc software versions and flag builds below libdigidocpp 4.2.1, DigiDoc4 4.8.2, DigiDoc Android 2.7.2, and DigiDoc iOS 2.8.1.
- Re-verify high-value signed documents processed by legacy clients using an updated DigiDoc release to compare validation results.
- Monitor for delivery of DigiDoc containers via email or messaging where the sender profile does not match expected business counterparties.
Monitoring Recommendations
- Enable endpoint software inventory reporting to continuously track DigiDoc client versions across the estate.
- Log signature validation outcomes centrally where DigiDoc is integrated with document workflows or e-service backends.
- Alert on execution of outdated DigiDoc binaries after a patch deadline has passed.
How to Mitigate CVE-2026-59112
Immediate Actions Required
- Update libdigidocpp to 4.2.1 or later on all systems that embed the library.
- Upgrade DigiDoc4 desktop clients to 4.8.2 or later on Windows and macOS endpoints.
- Update DigiDoc for Android to 2.7.2 and DigiDoc for iOS to 2.8.1 across managed mobile devices.
- Re-validate any legally significant signatures processed during the vulnerable window using a patched client.
Patch Information
RIA has released fixed versions across the DigiDoc product line. Refer to the ID.ee Software Update Recommendation for official guidance and download links, and to GitHub Pull Request #690 for the source-level fix in libdigidocpp.
Workarounds
- Restrict opening of DigiDoc containers to trusted senders until all clients are updated.
- For enterprise integrations, deploy the patched libdigidocpp library to backend signature-validation services before returning results to relying parties.
- Use mobile device management to enforce minimum required versions of the DigiDoc apps on Android and iOS.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
