CVE-2026-9058: Szafir SDK Auth Bypass Vulnerability

CVE-2026-9058 Overview

CVE-2026-9058 is a critical authentication bypass vulnerability in the Szafir SDK, a software development kit used for cryptographic digital signature verification. The SDK returns a success status code (Result/@code == 0, "Positively verified") even when the trust status of the signer's certificate cannot be established. Applications consuming the SDK incorrectly treat signatures as valid despite an unverified certificate chain. Attackers can exploit this flaw to impersonate users and bypass authentication mechanisms that rely on the SDK's verification output. The vulnerability is tracked under [CWE-393: Return of Wrong Status Code] and was fixed in version 463.

Critical Impact
Attackers can forge digital signatures and bypass authentication in any application relying on Szafir SDK for signature validation, enabling user impersonation across affected workflows.

Affected Products

Szafir SDK versions prior to 463
Applications integrating Szafir SDK for digital signature verification
Polish electronic signature ecosystem consumers (see Elektroniczny Podpis Resource)

Discovery Timeline

2026-05-25 - CVE-2026-9058 published to NVD
2026-05-26 - Last updated in NVD database

Technical Details for CVE-2026-9058

Vulnerability Analysis

The vulnerability stems from incorrect status code handling within the Szafir SDK's signature verification logic. When the SDK processes a digital signature, it produces an XML result document containing both a verification result code and a certificate type indicator. The SDK returns /VerifyingTaskItem/Signature/VerificationResult/Result/@code == 0, signaling "Positively verified," even when /VerifyingTaskItem/Signature/VerificationResult/SigningCertificate/@certificateType == "nondetermined". The nondetermined certificate type indicates the trust status of the signer's certificate could not be established. Consuming applications typically read only the top-level result code and treat the signature as cryptographically valid and trust-anchored.

Root Cause

The defect is a classification flaw mapped to [CWE-393]. The SDK conflates two distinct verification outcomes: cryptographic integrity of the signature and trust validation of the signing certificate chain. A signature can be mathematically correct while the certificate chain remains unverified. The SDK should return a non-success status when the certificate type is nondetermined. Instead, it surfaces a positive result, suppressing the trust failure from downstream consumers.

Attack Vector

An attacker constructs a document signed with a certificate that does not chain to a trusted root recognized by the relying application. Because the certificate path validation produces a nondetermined outcome rather than a hard failure, the SDK still emits a success code. The relying application processes the document as authentically signed by the certificate subject, enabling impersonation in authentication flows, signed-document workflows, and transaction approvals. The attack requires no privileges and no user interaction beyond standard document submission.

Detailed technical analysis is available in the CERT PL CVE-2026-9058 Analysis.

Detection Methods for CVE-2026-9058

Indicators of Compromise

Verification result XML containing Result/@code == 0 paired with SigningCertificate/@certificateType == "nondetermined"
Authentication or signing events using certificates that do not chain to a trusted enterprise or qualified trust list root
Unexpected successful signature validations from external or unknown certificate authorities

Detection Strategies

Parse verification result XML in consuming applications and reject any result where certificateType equals nondetermined, regardless of the top-level result code
Audit application logs for signature verifications that succeeded against certificates outside the expected trust anchors
Implement secondary certificate path validation independent of the SDK's reported result

Monitoring Recommendations

Centralize Szafir SDK verification logs and alert on certificateType="nondetermined" occurrences
Track Szafir SDK version inventory across endpoints and servers, flagging any version below 463
Monitor authentication systems that consume Szafir signatures for spikes in successful logins from new or unexpected certificate issuers

How to Mitigate CVE-2026-9058

Immediate Actions Required

Upgrade Szafir SDK to version 463 or later on all systems performing signature verification
Inventory every application and service that links against Szafir SDK and prioritize patching for authentication-critical workflows
Review recent signature verification logs for nondetermined certificate outcomes that were treated as successful

Patch Information

The vendor fixed the issue in Szafir SDK version 463. Upgrading is the authoritative remediation. Refer to the CERT PL CVE-2026-9058 Analysis for vendor coordination details and downloadable updates via the Elektroniczny Podpis Resource.

Workarounds

Add application-level validation that rejects any verification result where SigningCertificate/@certificateType is not explicitly trusted, even when the result code is 0
Enforce an allowlist of acceptable certificate issuers within consuming applications until patching completes
Disable signature-based authentication paths that cannot enforce strict certificate chain validation until the SDK is upgraded

bash

# Example application-side guard (pseudocode)
# Reject verification results whose certificateType is not explicitly trusted
if [ "$result_code" = "0" ] && [ "$certificate_type" = "nondetermined" ]; then
  echo "Reject: signature valid but certificate trust not established"
  exit 1
fi