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Lemmy: Rate limit bypass via X-Forwarded-For header spoofing in actix-web ConnectionInfo

Type: advisorySources: OSV

Lemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-beta.1, actix-web ConnectionInfo::realip_remote_addr reads the first value of X-Forwarded-For as the client address used by raw_ip_key in crates/utils/src/rate_limit/mod.rs. Lemmy's bundled docker/nginx.conf uses $proxy_add_x_forwarded_for instead of $remote_addr, which appends the real client address to an X-Forwarded-For value supplied by the client. An unauthenticated attacker can therefore place a different spoofed address first on each request and receive a new rate-limit bucket, bypassing limits on POST /api/v4/account/auth/register, POST /api/v4/account/auth/login, POST /api/v4/post, POST /api/v4/comment, GET /api/v4/search, POST /api/v4/image, and POST /api/v4/account/import_settings. This permits excessive account creation, brute-force attempts, spam, scraping, uploads, and repeated imports. This issue is fixed in versions 0.19.19 and 1.0.0-beta.1.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-54738
Confirmed fixed CVEs
Not specified
Updated in this feed
4 Nov 2026, 18:32 UTC · Revision 1

Source evidence

Lemmy: Rate limit bypass via X-Forwarded-For header spoofing in actix-web ConnectionInfo

core-osv · Original source

Published 19 Aug 2026, 20:27 UTC

Lemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-beta.1, actix-web ConnectionInfo::realip_remote_addr reads the first value of X-Forwarded-For as the client address used by raw_ip_key in crates/utils/src/rate_limit/mod.rs. Lemmy's bundled docker/nginx.conf uses $proxy_add_x_forwarded_for instead of $remote_addr, which appends the real client address to an X-Forwarded-For value supplied by the client. An unauthenticated attacker can therefore place a different spoofed address first on each request and receive a new rate-limit bucket, bypassing limits on POST /api/v4/account/auth/register, POST /api/v4/account/auth/login, POST /api/v4/post, POST /api/v4/comment, GET /api/v4/search, POST /api/v4/image, and POST /api/v4/account/import_settings. This permits excessive account creation, brute-force attempts, spam, scraping, uploads, and repeated imports. This issue is fixed in versions 0.19.19 and 1.0.0-beta.1.

osv:CVE-2026-54738
Complete source record
{
  "id": "3f0408f039f6354900385c9dff47480e683bdf4f654acf560b42130e65a4ccdf",
  "url": "https://osv.dev/vulnerability/CVE-2026-54738",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Lemmy: Rate limit bypass via X-Forwarded-For header spoofing in actix-web ConnectionInfo",
    "summary": "Lemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-beta.1, actix-web ConnectionInfo::realip_remote_addr reads the first value of X-Forwarded-For as the client address used by raw_ip_key in crates/utils/src/rate_limit/mod.rs. Lemmy's bundled docker/nginx.conf uses $proxy_add_x_forwarded_for instead of $remote_addr, which appends the real client address to an X-Forwarded-For value supplied by the client. An unauthenticated attacker can therefore place a different spoofed address first on each request and receive a new rate-limit bucket, bypassing limits on POST /api/v4/account/auth/register, POST /api/v4/account/auth/login, POST /api/v4/post, POST /api/v4/comment, GET /api/v4/search, POST /api/v4/image, and POST /api/v4/account/import_settings. This permits excessive account creation, brute-force attempts, spam, scraping, uploads, and repeated imports. This issue is fixed in versions 0.19.19 and 1.0.0-beta.1.",
    "evidence": "osv:CVE-2026-54738",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-54738",
      "aliases": [
        "CVE-2026-54738",
        "GHSA-2hrg-7x4g-9vpg"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/lemmynet/lemmy",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "f6e986e7e54d456aa1ffec38f1576c5bb15e0afd"
                },
                {
                  "introduced": "87cbc2f3702bde803b313161321306a37af6ae3e"
                },
                {
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                },
                {
                  "fixed": "41513c89ceecee719bff05acfe613e3b1e85f23c"
                },
                {
                  "fixed": "8b5b2aa78417b53ff3622c01f5bed2f1590f3b82"
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              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
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                      {
                        "fixed": "0.19.19"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "introduced": "1.0.0-alpha.5"
                      },
                      {
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                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
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                      {
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                    "source": "REFERENCES_COMMIT"
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                  {
                    "range": [
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                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "f6e986e7e54d456aa1ffec38f1576c5bb15e0afd"
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                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "0.19.19"
                  },
                  {
                    "range": [
                      {
                        "fixed": "fe8b39b10bb70e9c0edca2df7a63c8f8d4059c98"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "1.0.0-beta.1"
                  }
                ]
              }
            }
          ],
          "versions": [
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          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-54738.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:38.475785427Z",
      "provider": "osv",
      "references": [
        "https://github.com/LemmyNet/lemmy/releases/tag/0.19.19",
        "https://github.com/LemmyNet/lemmy/releases/tag/1.0.0-beta.1",
        "https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54738.json",
        "https://github.com/LemmyNet/lemmy/security/advisories/GHSA-2hrg-7x4g-9vpg",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-54738",
        "https://github.com/LemmyNet/lemmy/commit/41513c89ceecee719bff05acfe613e3b1e85f23c",
        "https://github.com/LemmyNet/lemmy/commit/8b5b2aa78417b53ff3622c01f5bed2f1590f3b82",
        "https://github.com/LemmyNet/lemmy/pull/6574",
        "https://github.com/LemmyNet/lemmy/pull/6575"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-799"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54738.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-54738",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 505728,
  "published_at": "2026-08-19T20:27:45.162+00:00"
}