CVE-2025-66199

Publication date 27 January 2026

Last updated 28 January 2026

Ubuntu priority

Low

Why this priority?

Description

Issue summary: A TLS 1.3 connection using certificate compression can be forced to allocate a large buffer before decompression without checking against the configured certificate size limit. Impact summary: An attacker can cause per-connection memory allocations of up to approximately 22 MiB and extra CPU work, potentially leading to service degradation or resource exhaustion (Denial of Service). In affected configurations, the peer-supplied uncompressed certificate length from a CompressedCertificate message is used to grow a heap buffer prior to decompression. This length is not bounded by the max_cert_list setting, which otherwise constrains certificate message sizes. An attacker can exploit this to cause large per-connection allocations followed by handshake failure. No memory corruption or information disclosure occurs. This issue only affects builds where TLS 1.3 certificate compression is compiled in (i.e., not OPENSSL_NO_COMP_ALG) and at least one compression algorithm (brotli, zlib, or zstd) is available, and where the compression extension is negotiated. Both clients receiving a server CompressedCertificate and servers in mutual TLS scenarios receiving a client CompressedCertificate are affected. Servers that do not request client certificates are not vulnerable to client-initiated attacks. Users can mitigate this issue by setting SSL_OP_NO_RX_CERTIFICATE_COMPRESSION to disable receiving compressed certificates. The FIPS modules in 3.6, 3.5, 3.4 and 3.3 are not affected by this issue, as the TLS implementation is outside the OpenSSL FIPS module boundary. OpenSSL 3.6, 3.5, 3.4 and 3.3 are vulnerable to this issue. OpenSSL 3.0, 1.1.1 and 1.0.2 are not affected by this issue.

Read the notes from the security team

Why is this CVE low priority?

OpenSSL developers have rated this issue to be low severity

Learn more about Ubuntu priority

Status

Package Ubuntu Release Status
openssl 25.10 questing
Fixed 3.5.3-1ubuntu3
25.04 plucky Ignored end of life, was needed
24.04 LTS noble
Not affected
22.04 LTS jammy  
Not affected
20.04 LTS focal  
Not affected
18.04 LTS bionic  
Not affected
16.04 LTS xenial  
Not affected
14.04 LTS trusty
Not affected
openssl1.0 25.10 questing Not in release
25.04 plucky Not in release
24.04 LTS noble Not in release
22.04 LTS jammy Not in release
18.04 LTS bionic
Not affected
nodejs 25.10 questing
Not affected
25.04 plucky
Not affected
24.04 LTS noble
Not affected
22.04 LTS jammy
Vulnerable
20.04 LTS focal
Not affected
18.04 LTS bionic
Needs evaluation
16.04 LTS xenial
Needs evaluation
14.04 LTS trusty
Not affected
edk2 25.10 questing
Needs evaluation
25.04 plucky Ignored end of life, was needs-triage
24.04 LTS noble
Needs evaluation
22.04 LTS jammy
Not affected
20.04 LTS focal
Not affected
18.04 LTS bionic
Not affected
16.04 LTS xenial
Not affected

Notes

mdeslaur

edk2 in jammy embeds OpenSSL 1.1.1j edk2 in noble embeds OpenSSL 3.0.9 edk2 in plucky embeds OpenSSL 3.4.0 edk2 in questing embeds OpenSSL 3.4.0 3.3.x and higher only

References

Related Ubuntu Security Notices (USN)

    • USN-7980-1
    • OpenSSL vulnerabilities
    • 27 January 2026

Other references