CVE-2025-66199

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 maxcertlist 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 OPENSSLNOCOMP_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 SSLOPNORXCERTIFICATE_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.

References

Affected packages

Git / github.com/openssl/openssl

Affected ranges

Type

GIT

Repo

https://github.com/openssl/openssl

Events

Introduced

4cb31128b5790819dfeea2739fbde265f71a10a2

Fixed

4601ff25acd6c2fe58a8bfe241e6c470e27b8074

Introduced

98acb6b02839c609ef5b837794e08d906d965335

Fixed

565bdcc41bbf89fcbaf962636469332689f0c9fd

Introduced

636dfadc70ce26f2473870570bfd9ec352806b1d

Fixed

67b5686b4419b4cb8caa502711c41815f5279751

Introduced

7b371d80d959ec9ab4139d09d78e83c090de9779

Fixed

c9a9e5b10105ad850b6e4d1122c645c67767c341

Fixed

3ed1f75249932b155eef993a8e66a99cb98bfef4

Fixed

6184a4fb08ee6d7bca570d931a4e8bef40b64451

Fixed

895150b5e021d16b52fb32b97e1dd12f20448be5

Fixed

966a2478046c311ed7dae50c457d0db4cafbf7e4

Database specific

{
    "versions": [
        {
            "introduced": "3.3.0"
        },
        {
            "fixed": "3.3.6"
        },
        {
            "introduced": "3.4.0"
        },
        {
            "fixed": "3.4.4"
        },
        {
            "introduced": "3.5.0"
        },
        {
            "fixed": "3.5.5"
        },
        {
            "introduced": "3.6.0"
        },
        {
            "fixed": "3.6.1"
        }
    ]
}

Affected versions

3.*

3.3-POST-CLANG-FORMAT-WEBKIT

3.3-PRE-CLANG-FORMAT-WEBKIT

3.4-POST-CLANG-FORMAT-WEBKIT

3.4-PRE-CLANG-FORMAT-WEBKIT

3.5-POST-CLANG-FORMAT-WEBKIT

3.5-PRE-CLANG-FORMAT-WEBKIT

3.6-POST-CLANG-FORMAT-WEBKIT

3.6-PRE-CLANG-FORMAT-WEBKIT

openssl-3.*

openssl-3.3.0

openssl-3.3.1

openssl-3.3.2

openssl-3.3.3

openssl-3.3.4

openssl-3.3.5

openssl-3.4.0

openssl-3.4.1

openssl-3.4.2

openssl-3.4.3

openssl-3.5.0

openssl-3.5.1

openssl-3.5.2

openssl-3.5.3

openssl-3.5.4

openssl-3.6.0

Database specific

source

"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-66199.json"

vanir_signatures

[
    {
        "signature_type": "Function",
        "source": "https://github.com/openssl/openssl/commit/966a2478046c311ed7dae50c457d0db4cafbf7e4",
        "id": "CVE-2025-66199-041c93f5",
        "deprecated": false,
        "target": {
            "function": "tls13_process_compressed_certificate",
            "file": "ssl/statem/statem_lib.c"
        },
        "signature_version": "v1",
        "digest": {
            "length": 1935.0,
            "function_hash": "270485391765080273460682519899044817772"
        }
    },
    {
        "signature_type": "Function",
        "source": "https://github.com/openssl/openssl/commit/3ed1f75249932b155eef993a8e66a99cb98bfef4",
        "id": "CVE-2025-66199-4a813541",
        "deprecated": false,
        "target": {
            "function": "tls13_process_compressed_certificate",
            "file": "ssl/statem/statem_lib.c"
        },
        "signature_version": "v1",
        "digest": {
            "length": 1935.0,
            "function_hash": "270485391765080273460682519899044817772"
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    },
    {
        "signature_type": "Line",
        "source": "https://github.com/openssl/openssl/commit/966a2478046c311ed7dae50c457d0db4cafbf7e4",
        "id": "CVE-2025-66199-51b53a28",
        "deprecated": false,
        "target": {
            "file": "ssl/statem/statem_lib.c"
        },
        "signature_version": "v1",
        "digest": {
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            "threshold": 0.9
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        "signature_type": "Line",
        "source": "https://github.com/openssl/openssl/commit/6184a4fb08ee6d7bca570d931a4e8bef40b64451",
        "id": "CVE-2025-66199-c90fdcc3",
        "deprecated": false,
        "target": {
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        },
        "signature_version": "v1",
        "digest": {
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    {
        "signature_type": "Function",
        "source": "https://github.com/openssl/openssl/commit/895150b5e021d16b52fb32b97e1dd12f20448be5",
        "id": "CVE-2025-66199-cf35db1d",
        "deprecated": false,
        "target": {
            "function": "tls13_process_compressed_certificate",
            "file": "ssl/statem/statem_lib.c"
        },
        "signature_version": "v1",
        "digest": {
            "length": 1935.0,
            "function_hash": "270485391765080273460682519899044817772"
        }
    },
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        "signature_type": "Line",
        "source": "https://github.com/openssl/openssl/commit/3ed1f75249932b155eef993a8e66a99cb98bfef4",
        "id": "CVE-2025-66199-f67dd36f",
        "deprecated": false,
        "target": {
            "file": "ssl/statem/statem_lib.c"
        },
        "signature_version": "v1",
        "digest": {
            "line_hashes": [
                "66607492443430939978305191189939209227",
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            "threshold": 0.9
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        "signature_type": "Function",
        "source": "https://github.com/openssl/openssl/commit/6184a4fb08ee6d7bca570d931a4e8bef40b64451",
        "id": "CVE-2025-66199-f9443673",
        "deprecated": false,
        "target": {
            "function": "tls13_process_compressed_certificate",
            "file": "ssl/statem/statem_lib.c"
        },
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        "digest": {
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            "function_hash": "82643088808423643955393758377693009659"
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    },
    {
        "signature_type": "Line",
        "source": "https://github.com/openssl/openssl/commit/895150b5e021d16b52fb32b97e1dd12f20448be5",
        "id": "CVE-2025-66199-fbbbd1ad",
        "deprecated": false,
        "target": {
            "file": "ssl/statem/statem_lib.c"
        },
        "signature_version": "v1",
        "digest": {
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]