Description

SWUpdate through 2026.05.1 contains an improper certificate validation vulnerability in crypto/swupdate_cms_verify_openssl.c that trusts untrusted X.509 certificates embedded in CMS SignedData for chain building. Attackers holding a signing key from a sibling intermediate under the same root can embed that intermediate in the signature to install malicious updates.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.1",
  "pubDate": "2026-10-12T16:17:05.557Z",
  "pubdate": "2026-10-12T16:17:05.557Z",
  "executiveSummary": "The SWUpdate utility, up to version 2026.05.1, contains a critical improper certificate validation vulnerability within its CMS signature verification logic. This flaw allows for the unauthorized installation of malicious updates due to a failure in properly restricting the trust chain during the verification of CMS SignedData.\nThe vulnerability is classified as an improper certificate validation issue. It enables an attacker who possesses a signing key from a sibling intermediate CA—sharing the same root as the authorized signer—to craft a malicious update package. By embedding the unauthorized sibling intermediate certificate within the CMS signature, the attacker can force the SWUpdate verification process to build a valid trust chain back to the root CA.\nThe primary impact is the complete compromise of the update mechanism, allowing for arbitrary code execution or the installation of malicious software on the target device. This vulnerability poses a significant risk to the integrity of the update process, as it bypasses intended security controls. Exploitation requires the attacker to possess a legitimate signing key from a sibling intermediate certificate, making it particularly dangerous in environments where multiple organizations or sub-entities operate under a common root authority.",
  "technicalDetails": "The root cause of this vulnerability lies in the implementation of the CMS signature verification process within 'crypto/swupdate_cms_verify_openssl.c'. The software incorrectly trusts X.509 certificates that are provided within the 'SignedData' structure of the CMS package when attempting to construct a certification path.\nIn a secure implementation, an update agent should strictly validate the update's signature against a predefined, trusted certificate or a restricted certificate store. However, SWUpdate's current verification logic is susceptible to chain building manipulation. When processing a signed update, the affected code uses the OpenSSL backend to verify the signature. Because the logic accepts certificates embedded within the CMS payload for chain construction, it does not sufficiently verify that the provided certificate is the one explicitly authorized to sign updates for the specific target device.\nThe attack flow proceeds as follows: First, the attacker obtains a signing key issued by an intermediate certificate authority that resides under the same root certificate as the legitimate update signer. Because both the attacker's intermediate and the authorized signer's certificate share the same root, the SWUpdate verification engine perceives the attacker's intermediate as a valid branch of the root-of-trust. Second, the attacker packages a malicious firmware or software update. Third, the attacker embeds the unauthorized sibling intermediate certificate into the CMS SignedData section of the malicious update file. Finally, the attacker triggers the update process. During verification, the SWUpdate utility retrieves the attacker-provided intermediate certificate from the CMS structure, uses it to build a valid path to the root CA, and subsequently verifies the malicious signature using the attacker's key.\nBecause the logic fails to enforce constraints that would prevent 'sibling' certificate authorities from acting as valid signers, the signature verification check returns a successful result despite the origin of the update being unauthorized. This bypass leads to the installation of malicious payloads with the same privileges as the SWUpdate process, typically resulting in full device compromise.\nThis vulnerability affects all SWUpdate versions up to and including 2026.05.1. The attack is restricted to entities possessing a valid signing key from a trusted sibling, but it requires no further interaction once the malicious update is delivered to the device update agent."
}