CVE-2026-71887
Description
A flaw was found in Bouncy Castle. The high-level OpenPGP (Pretty Good Privacy) API fails to properly enforce cross-certification requirements when validating subkeys that omit key capability flags. A remote attacker can exploit this flaw by binding a victim's public signing key to an attacker-controlled primary key, causing verifiers to mistakenly attribute genuinely signed messages to the attacker.
Statement
Red Hat has evaluated this vulnerability as having an Important severity rating because remote actors can induce relying services to misattribute authentic digital signatures to an arbitrary identity without requiring credentials or private key compromise. Applications utilizing Bouncy Castle's high-level OpenPGP verification mechanisms may validate a re-bound signing subkey as trusted under an attacker-specified certificate. While this flaw does not permit forging arbitrary signatures or exposing private keys, downstream systems relying on signature identity assertions suffer significant integrity compromise.
Mitigation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | None | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | None | N/A | N/A |
| Integrity Impact | High | N/A | N/A |
| Availability Impact | None | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Understanding the Weakness (CWE)
Integrity,Authentication
Technical Impact: Bypass Protection Mechanism; Gain Privileges or Assume Identity
When a certificate is invalid or malicious, it might allow an attacker to spoof a trusted entity by interfering in the communication path between the host and client. The product might connect to a malicious host while believing it is a trusted host, or the product might be deceived into accepting spoofed data that appears to originate from a trusted host.
Frequently Asked Questions
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