CVE-2026-53939 OpenIDC/cjose uses all-zero Content Encryption Key for AES-CBC-HMAC JWE encryption
Attackers can decrypt and forge JWE tokens because the library uses an all-zero key for AES-CBC-HMAC encryption, compromising confidentiality and integrity.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-53939?
CVE-2026-53939 is a critical vulnerability in OpenIDC cjose, published on 8 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
OpenIDC/cjose is a C library implementing the Javascript Object Signing and Encryption (JOSE). In versions 0.6.1 through 0.6.2.5, when cjose encrypts a JWE using an AES-CBC-HMAC content-encryption algorithm (`A128CBC-HS256`, `A192CBC-HS384`, or `A256CBC-HS512`) together with any key-management algorithm that generates a fresh content-encryption key (CEK), the CEK is all zero bytes instead of being randomly generated. The resulting JWE is therefore encrypted and authenticated under a fixed, publicly known key, so anyone who obtains the JWE can recover the plaintext and forge or modify the content. This is fixed in version 0.6.2.6 by `_cjose_jwe_set_cek_aes_cbc()` generating the CEK from `RAND_bytes`. A regression test asserts that the `encrypted_key` differs across two encryptions for each AES-CBC-HMAC variant. Until upgrading, for data encrypted with cjose, three options are available. Use an AES-GCM `enc` (`A128GCM` / `A192GCM` / `A256GCM`) instead of an AES-CBC-HMAC `enc`, use `alg=dir` with a caller-supplied CEK, or avoid using cjose for JWE encryption with the affected algorithm pair. These are mitigations for new ciphertexts only; data already encrypted under the zero key remains compromised and should be re-encrypted (and any secrets it contained rotated).
Which versions are affected by CVE-2026-53939?
Linux distribution packages (17)
cjose AlmaLinux:10 | All versions | 0.6.2.2-7.el10_2.2 |
cjose-devel AlmaLinux:10 | All versions | 0.6.2.2-7.el10_2.2 |
cjose AlmaLinux:8 | All versions | 0.6.1-6.module_el8.10.0+4330+15616d81 |
cjose-devel AlmaLinux:8 | All versions | 0.6.1-6.module_el8.10.0+4330+15616d81 |
mod_auth_openidc AlmaLinux:8 | All versions | 2.4.9.4-9.module_el8.10.0+4297+63ae3533 |
cjose AlmaLinux:9 | All versions | 0.6.1-17.el9_8.2 |
cjose-devel AlmaLinux:9 | All versions | 0.6.1-17.el9_8.2 |
cjose Red Hat:enterprise_linux:10.2 | All versions | 0:0.6.2.2-7.el10_2.2 |
cjose-debuginfo Red Hat:enterprise_linux:10.2 | All versions | 0:0.6.2.2-7.el10_2.2 |
cjose-debugsource Red Hat:enterprise_linux:10.2 | All versions | 0:0.6.2.2-7.el10_2.2 |
cjose-devel Red Hat:enterprise_linux:10.2 | All versions | 0:0.6.2.2-7.el10_2.2 |
cjose Red Hat:enterprise_linux_eus:10.0 | All versions | 0:0.6.2.2-7.el10_0.2 |
cjose-debuginfo Red Hat:enterprise_linux_eus:10.0 | All versions | 0:0.6.2.2-7.el10_0.2 |
cjose-debugsource Red Hat:enterprise_linux_eus:10.0 | All versions | 0:0.6.2.2-7.el10_0.2 |
cjose-devel Red Hat:enterprise_linux_eus:10.0 | All versions | 0:0.6.2.2-7.el10_0.2 |
cjose Rocky Linux:10 | All versions | 0:0.6.2.2-7.el10_2.2 |
mod_auth_openidc Rocky Linux:8 | All versions | 0:2.4.9.4-9.module+el8.10.0+40373+8a3f15d2 |
How do I fix CVE-2026-53939?
Upgrade to a fixed version.
Is CVE-2026-53939 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-53939 exists.
Sources
Also known as ALSA-2026:80605, ALSA-2026:92145, ALSA-2026:92157, AZL-101096, CLSA-2026-1792632603, DEBIAN-CVE-2026-53939 and 6 more.