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

0 Unknown introduced commit / All previous commits are affected

Fixed

3ed1f75249932b155eef993a8e66a99cb98bfef4

Fixed

6184a4fb08ee6d7bca570d931a4e8bef40b64451

Fixed

895150b5e021d16b52fb32b97e1dd12f20448be5

Fixed

966a2478046c311ed7dae50c457d0db4cafbf7e4

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

Other

BEFORE_engine

OpenSSL_0_9_1c

OpenSSL_0_9_2b

OpenSSL_0_9_3

OpenSSL_0_9_3a

OpenSSL_0_9_3beta2

OpenSSL_0_9_4

OpenSSL_0_9_5a

OpenSSL_0_9_5a-beta1

OpenSSL_0_9_5a-beta2

OpenSSL_0_9_5beta1

OpenSSL_0_9_5beta2

OpenSSL_0_9_6-beta3

OpenSSL_1_1_0-pre1

OpenSSL_1_1_0-pre2

OpenSSL_1_1_0-pre3

OpenSSL_1_1_0-pre4

OpenSSL_1_1_0-pre5

OpenSSL_1_1_0-pre6

OpenSSL_1_1_1

OpenSSL_1_1_1-pre1

OpenSSL_1_1_1-pre2

OpenSSL_1_1_1-pre3

OpenSSL_1_1_1-pre4

OpenSSL_1_1_1-pre5

OpenSSL_1_1_1-pre6

OpenSSL_1_1_1-pre7

OpenSSL_1_1_1-pre8

OpenSSL_1_1_1-pre9

master-post-auto-reformat

master-post-reformat

master-pre-auto-reformat

master-pre-reformat

openssl-3.*

openssl-3.0.0-alpha1

openssl-3.0.0-alpha10

openssl-3.0.0-alpha11

openssl-3.0.0-alpha12

openssl-3.0.0-alpha13

openssl-3.0.0-alpha14

openssl-3.0.0-alpha15

openssl-3.0.0-alpha16

openssl-3.0.0-alpha17

openssl-3.0.0-alpha2

openssl-3.0.0-alpha3

openssl-3.0.0-alpha4

openssl-3.0.0-alpha5

openssl-3.0.0-alpha6

openssl-3.0.0-alpha7

openssl-3.0.0-alpha8

openssl-3.0.0-alpha9

openssl-3.0.0-beta1

openssl-3.0.0-beta2

openssl-3.2.0-alpha1

openssl-3.2.0-alpha2

openssl-3.3.0

openssl-3.3.0-alpha1

openssl-3.3.0-beta1

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-3.4.0-alpha1

openssl-3.4.0-beta1

openssl-3.4.1

openssl-3.4.2

openssl-3.4.3

openssl-3.5.0

openssl-3.5.0-alpha1

openssl-3.5.0-beta1

openssl-3.5.1

openssl-3.5.2

openssl-3.5.3

openssl-3.5.4

openssl-3.6.0

openssl-3.6.0-alpha1

openssl-3.6.0-beta1

Database specific

source

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

vanir_signatures

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