CVE-2025-66199
TLS 1.3 CompressedCertificate excessive memory allocation
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.
INFO
Published Date :
Jan. 27, 2026, 4:16 p.m.
Last Modified :
Feb. 2, 2026, 6:37 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | 134c704f-9b21-4f2e-91b3-4a467353bcc0 |
Solution
- Disable receiving compressed certificates using SSL_OP_NO_RX_CERTIFICATE_COMPRESSION.
- Update to a non-vulnerable version of OpenSSL.
- Ensure TLS 1.3 is configured without compression.
- Limit certificate sizes to prevent excessive memory allocation.
Public PoC/Exploit Available at Github
CVE-2025-66199 has a 1 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2025-66199.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2025-66199 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2025-66199
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
使用Google Gemini API，对hacker news Top100文章总结摘要并翻译成体中文，每日自动更新。
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Ruby Shell Python
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2025-66199 vulnerability anywhere in the article.
-
CybersecurityNews
OpenSSL Vulnerabilities Allow Remote Attackers to Execute Malicious Code
OpenSSL patched 12 vulnerabilities on January 27, 2026, including one high-severity flaw that could lead to remote code execution. Most issues cause denial-of-service attacks but highlight risks in pa ... Read more
-
Daily CyberSecurity
Pre-Auth RCE Risk: OpenSSL Patches High-Severity Stack Overflow (CVE-2025-15467)
The maintainers of OpenSSL, the cryptographic library that underpins a vast portion of the secure web, have released a sweeping security update to address a dozen vulnerabilities ranging from memory c ... Read more
The following table lists the changes that have been made to the
CVE-2025-66199 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Feb. 02, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 3.3.0 up to (excluding) 3.3.6 *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 3.4.0 up to (excluding) 3.4.4 *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 3.5.0 up to (excluding) 3.5.5 *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 3.6.0 up to (excluding) 3.6.1 Added Reference Type OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/3ed1f75249932b155eef993a8e66a99cb98bfef4 Types: Patch Added Reference Type OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/6184a4fb08ee6d7bca570d931a4e8bef40b64451 Types: Patch Added Reference Type OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/895150b5e021d16b52fb32b97e1dd12f20448be5 Types: Patch Added Reference Type OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/966a2478046c311ed7dae50c457d0db4cafbf7e4 Types: Patch Added Reference Type OpenSSL Software Foundation: https://openssl-library.org/news/secadv/20260127.txt Types: Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jan. 29, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H -
New CVE Received by [email protected]
Jan. 27, 2026
Action Type Old Value New Value Added 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. Added CWE CWE-789 Added Reference https://github.com/openssl/openssl/commit/3ed1f75249932b155eef993a8e66a99cb98bfef4 Added Reference https://github.com/openssl/openssl/commit/6184a4fb08ee6d7bca570d931a4e8bef40b64451 Added Reference https://github.com/openssl/openssl/commit/895150b5e021d16b52fb32b97e1dd12f20448be5 Added Reference https://github.com/openssl/openssl/commit/966a2478046c311ed7dae50c457d0db4cafbf7e4 Added Reference https://openssl-library.org/news/secadv/20260127.txt