libdigidocpp CVE-2026-59112

Exploitation requires the victim to actively open (UI:A) a maliciously crafted BDOC 2.1 or ASiC-E document using an unpatched DigiDoc client - specifically DigiDoc4 desktop 4.7.0-4.8.1, DigiDoc Android 2.7.0-2.7.1, or DigiDoc iOS 2.8.0 - on a local device (AV:L). The specific attack prerequisite (AT:P) is that the crafted document must contain a structural anomaly in the XAdES signature block capable of triggering a C++ exception within the validation path (for example, a malformed SignaturePolicyIdentifier, absent DigestMethod, or malformed Reference URI), and that no code around the call site catches this exception before it exits validate(). No authentication to any network service or external system is required; the vulnerability is entirely a client-side file-parsing issue. What limits exploitation: the attacker must deliver the crafted document to a specific victim through social engineering, phishing, or a file-sharing channel; the victim must voluntarily open the file using the vulnerable application; and the device must be running one of the affected application versions - there is no remote code execution primitive and no network-reachable attack surface.

The CVSS 4.0 score of 4.4 Medium reflects real exploitation constraints: local attack vector (AV:L), mandatory active user interaction (UI:A), and specific attack prerequisites (AT:P) collectively prevent opportunistic or mass exploitation. Despite those constraints, the High integrity impact (VI:H) is particularly consequential in the DigiDoc context - these applications exist specifically to establish the legal validity of electronically signed documents, so a bypass that causes an invalid or forged signature to appear as verified strikes at the entire trust model, not a peripheral feature. No EPSS score was supplied and the CVE is absent from CISA KEV, so exploitation probability and confirmed in-the-wild activity are unknown beyond the E:P proof-of-concept signal. For any organization relying on DigiDoc-validated signatures for government, financial, or cross-border eIDAS document workflows - even a mid-sized municipal IT team in swidnica evaluating Baltic eIDAS interoperability would face material document-integrity risk if their DigiDoc client stack falls in the affected range - the moderate CVSS score understates the business impact of accepting a forged signature as legally valid. The limiting factor for broad exploitation is delivery: the attacker must socially engineer the victim into opening a crafted document with an unpatched client, which requires targeted effort rather than passive scanning.

An attacker constructs a BDOC 2.1 ASiC-E container with a deliberately malformed XAdES signature block - for example, a SignaturePolicyIdentifier or Reference element structured to trigger a C++ exception during policy or digest processing in libdigidocpp's SignatureXAdES_B::validate(). When the target opens the document in an unpatched DigiDoc4 desktop or DigiDoc mobile application, the exception escapes the validation routine without registering as a failure, and the application displays the document as bearing a valid, verified signature - allowing the attacker's unsigned or tampered content to be accepted as legally signed. A proof-of-concept is indicated by the CVSS 4.0 E:P exploit maturity modifier, though no public POC repository has been confirmed in the provided references.