CVE-2026-12803
AEAD nonce-binding bug in Bouncy Castle Java permits cross-nonce forgery.
Is CVE-2026-12803 being exploited?
Not confirmed. CVE-2026-12803 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.17% probability of exploitation in the next 30 days.
How severe is CVE-2026-12803?
CVE-2026-12803 is rated High with a CVSS score of 8.7. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-12803?
Yes. A fix has been recorded for CVE-2026-12803. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-12803 affect?
CVE-2026-12803 affects Bouncy Castle for Java < 1.85, Bouncy Castle for Java LTS < 2.73.12, Java apps using KCCMBlockCipher without AAD. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-12803?
Upgrade to Bouncy Castle >=1.85 or LTS >=2.73.12; ensure AAD is used and reject unauthenticated ciphertexts.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Cross-nonce AEAD forgery when AAD is absent: attackers can forge valid ciphertexts/tags, bypass integrity and inject or tamper messages.
Patch when possible
- affected< 1.85
- affected>= 2.73.0 and < 2.73.12
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.