CURL-CVE-2021-22947

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Source
https://curl.se/docs/CVE-2021-22947.html
Import Source
https://curl.se/docs/CURL-CVE-2021-22947.json
JSON Data
https://api.osv.dev/v1/vulns/CURL-CVE-2021-22947
Aliases
Published
2021-09-15T08:00:00Z
Modified
2026-05-27T02:29:07.664713Z
Summary
STARTTLS protocol injection via MITM
Details

When curl connects to an IMAP, POP3, SMTP or FTP server to exchange data securely using STARTTLS to upgrade the connection to TLS level, the server can still respond and send back multiple responses before the TLS upgrade. Such multiple pipelined responses are cached by curl. curl would then upgrade to TLS but not flush the in-queue of cached responses and instead use and trust the responses it got before the TLS handshake as if they were authenticated.

Using this flaw, it allows a Man-In-The-Middle attacker to first inject the fake responses, then pass-through the TLS traffic from the legitimate server and trick curl into sending data back to the user thinking the attacker's injected data comes from the TLS-protected server.

Over POP3 and IMAP an attacker can inject fake response data.

Database specific 
{
    "package": "curl",
    "URL": "https://curl.se/docs/CVE-2021-22947.json",
    "last_affected": "7.78.0",
    "issue": "https://hackerone.com/reports/1334763",
    "affects": "both",
    "severity": "Medium",
    "award": {
        "currency": "USD",
        "amount": "1500"
    },
    "www": "https://curl.se/docs/CVE-2021-22947.html",
    "CWE": {
        "desc": "Acceptance of Extraneous Untrusted Data With Trusted Data",
        "id": "CWE-349"
    }
}
References
Credits
    • Patrick Monnerat - FINDER
    • Patrick Monnerat - REMEDIATION_DEVELOPER

Affected packages

Git / github.com/curl/curl.git

Affected ranges

Type
SEMVER
Events
Introduced
7.20.0
Fixed
7.79.0
Type
GIT
Repo
https://github.com/curl/curl.git
Events
Introduced
ec3bb8f727405642a471b4b1b9eb0118fc003104
Fixed
8ef147c43646e91fdaad5d0e7b60351f842e5c68

Affected versions

7.*
7.20.0
7.20.1
7.21.0
7.21.1
7.21.2
7.21.3
7.21.4
7.21.5
7.21.6
7.21.7
7.22.0
7.23.0
7.23.1
7.24.0
7.25.0
7.26.0
7.27.0
7.28.0
7.28.1
7.29.0
7.30.0
7.31.0
7.32.0
7.33.0
7.34.0
7.35.0
7.36.0
7.37.0
7.37.1
7.38.0
7.39.0
7.40.0
7.41.0
7.42.0
7.42.1
7.43.0
7.44.0
7.45.0
7.46.0
7.47.0
7.47.1
7.48.0
7.49.0
7.49.1
7.50.0
7.50.1
7.50.2
7.50.3
7.51.0
7.52.0
7.52.1
7.53.0
7.53.1
7.54.0
7.54.1
7.55.0
7.55.1
7.56.0
7.56.1
7.57.0
7.58.0
7.59.0
7.60.0
7.61.0
7.61.1
7.62.0
7.63.0
7.64.0
7.64.1
7.65.0
7.65.1
7.65.2
7.65.3
7.66.0
7.67.0
7.68.0
7.69.0
7.69.1
7.70.0
7.71.0
7.71.1
7.72.0
7.73.0
7.74.0
7.75.0
7.76.0
7.76.1
7.77.0
7.78.0
Other
curl-7_20_0
curl-7_20_1
curl-7_21_0
curl-7_21_1
curl-7_21_2
curl-7_21_3
curl-7_21_4
curl-7_21_5
curl-7_21_6
curl-7_21_7
curl-7_22_0
curl-7_23_0
curl-7_23_1
curl-7_24_0
curl-7_25_0
curl-7_26_0
curl-7_27_0
curl-7_28_0
curl-7_28_1
curl-7_29_0
curl-7_30_0
curl-7_31_0
curl-7_32_0
curl-7_33_0
curl-7_34_0
curl-7_35_0
curl-7_36_0
curl-7_37_0
curl-7_37_1
curl-7_38_0
curl-7_39_0
curl-7_40_0
curl-7_41_0
curl-7_42_0
curl-7_42_1
curl-7_43_0
curl-7_44_0
curl-7_45_0
curl-7_46_0
curl-7_47_0
curl-7_47_1
curl-7_48_0
curl-7_49_0
curl-7_49_1
curl-7_50_0
curl-7_50_1
curl-7_50_2
curl-7_50_3
curl-7_51_0
curl-7_52_0
curl-7_52_1
curl-7_53_0
curl-7_53_1
curl-7_54_0
curl-7_54_1
curl-7_55_0
curl-7_55_1
curl-7_56_0
curl-7_56_1
curl-7_57_0
curl-7_58_0
curl-7_59_0
curl-7_60_0
curl-7_61_0
curl-7_61_1
curl-7_62_0
curl-7_63_0
curl-7_64_0
curl-7_64_1
curl-7_65_0
curl-7_65_1
curl-7_65_2
curl-7_65_3
curl-7_66_0
curl-7_67_0
curl-7_68_0
curl-7_69_0
curl-7_69_1
curl-7_70_0
curl-7_71_0
curl-7_71_1
curl-7_72_0
curl-7_73_0
curl-7_74_0
curl-7_75_0
curl-7_76_0
curl-7_76_1
curl-7_77_0
curl-7_78_0
tiny-curl-7_72_0

Database specific

source 
"https://curl.se/docs/CURL-CVE-2021-22947.json"
vanir_signatures_modified 
"2026-05-27T02:29:07Z"
vanir_signatures 
[
    {
        "target": {
            "file": "lib/pop3.c"
        },
        "id": "CURL-CVE-2021-22947-07f97260",
        "source": "https://github.com/curl/curl.git/commit/8ef147c43646e91fdaad5d0e7b60351f842e5c68",
        "signature_type": "Line",
        "deprecated": false,
        "digest": {
            "threshold": 0.9,
            "line_hashes": [
                "15818244023743251246121180721613206346",
                "264290710822608942509023658064866501305",
                "95783402388535053559558371031158626211"
            ]
        },
        "signature_version": "v1"
    },
    {
        "target": {
            "file": "lib/pop3.c",
            "function": "pop3_state_starttls_resp"
        },
        "id": "CURL-CVE-2021-22947-23d78c76",
        "source": "https://github.com/curl/curl.git/commit/8ef147c43646e91fdaad5d0e7b60351f842e5c68",
        "signature_type": "Function",
        "deprecated": false,
        "digest": {
            "length": 367.0,
            "function_hash": "156157676711957825618151761474403827986"
        },
        "signature_version": "v1"
    },
    {
        "target": {
            "file": "lib/ftp.c",
            "function": "ftp_statemachine"
        },
        "id": "CURL-CVE-2021-22947-3c3847ac",
        "source": "https://github.com/curl/curl.git/commit/8ef147c43646e91fdaad5d0e7b60351f842e5c68",
        "signature_type": "Function",
        "deprecated": false,
        "digest": {
            "length": 7667.0,
            "function_hash": "291176038097903092958094423929849484254"
        },
        "signature_version": "v1"
    },
    {
        "target": {
            "file": "lib/ftp.c"
        },
        "id": "CURL-CVE-2021-22947-6d773650",
        "source": "https://github.com/curl/curl.git/commit/8ef147c43646e91fdaad5d0e7b60351f842e5c68",
        "signature_type": "Line",
        "deprecated": false,
        "digest": {
            "threshold": 0.9,
            "line_hashes": [
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            ]
        },
        "signature_version": "v1"
    },
    {
        "target": {
            "file": "lib/imap.c",
            "function": "imap_state_starttls_resp"
        },
        "id": "CURL-CVE-2021-22947-8699633b",
        "source": "https://github.com/curl/curl.git/commit/8ef147c43646e91fdaad5d0e7b60351f842e5c68",
        "signature_type": "Function",
        "deprecated": false,
        "digest": {
            "length": 385.0,
            "function_hash": "30512939116690604190976008921301940171"
        },
        "signature_version": "v1"
    },
    {
        "target": {
            "file": "lib/imap.c"
        },
        "id": "CURL-CVE-2021-22947-d3bb20e0",
        "source": "https://github.com/curl/curl.git/commit/8ef147c43646e91fdaad5d0e7b60351f842e5c68",
        "signature_type": "Line",
        "deprecated": false,
        "digest": {
            "threshold": 0.9,
            "line_hashes": [
                "305664085898564189657251232396021201167",
                "247572126397743259643449771531197290285",
                "121358273080854664279798422557849661627"
            ]
        },
        "signature_version": "v1"
    },
    {
        "target": {
            "file": "lib/smtp.c"
        },
        "id": "CURL-CVE-2021-22947-de4c6649",
        "source": "https://github.com/curl/curl.git/commit/8ef147c43646e91fdaad5d0e7b60351f842e5c68",
        "signature_type": "Line",
        "deprecated": false,
        "digest": {
            "threshold": 0.9,
            "line_hashes": [
                "293265480734767209467846975422452335043",
                "185199186730252040051498636918179049257",
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            ]
        },
        "signature_version": "v1"
    },
    {
        "target": {
            "file": "lib/smtp.c",
            "function": "smtp_state_starttls_resp"
        },
        "id": "CURL-CVE-2021-22947-ee9fdf72",
        "source": "https://github.com/curl/curl.git/commit/8ef147c43646e91fdaad5d0e7b60351f842e5c68",
        "signature_type": "Function",
        "deprecated": false,
        "digest": {
            "length": 352.0,
            "function_hash": "69401027868289425349400319993836981190"
        },
        "signature_version": "v1"
    }
]