Lemmy: SSRF and internal image disclosure in post link metadata via unvalidated og:image
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Information disclosure
- Confidentiality · integrity · availability
- High · None · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-918 and the CVSS impact.
Summary
Lemmy is a link aggregator and forum for the fediverse. Prior to version 0.19.18, Lemmy fetches metadata for user-supplied post URLs and, under the default StoreLinkPreviews image mode, downloads the preview image through local pict-rs. While the top-level page URL is checked against internal IP ranges, the extracted og:image URL is not subject to the same restriction. As a result, an authenticated low-privileged user can submit an attacker-controlled public page whose Open Graph image points to an internal image endpoint. Lemmy will fetch that internal image server-side and store a local thumbnail that can then be served back to users. This issue has been patched in version 0.19.18.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| LemmyNet | lemmy | before 0.19.18 | 0.19.18 | Patch available | CNA |
| — | lemmy_api_common (crates.io) | before 0.19.18 | 0.19.18 | Patch available | GHSA-h6hf-9846-xwrq |
- lemmy VendorLemmyNet Affected before 0.19.18 Fixed in 0.19.18 Patch available CNA
- lemmy_api_common (crates.io) Vendor— Affected before 0.19.18 Fixed in 0.19.18 Patch available GHSA-h6hf-9846-xwrq
Remediation
- Fix · CNA lemmy (LemmyNet) Fixed in 0.19.18
- Fix · GHSA-h6hf-9846-xwrq lemmy_api_common (crates.io) Fixed in 0.19.18 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2026-42181
- 2026-10-03 Alias added: GHSA-h6hf-9846-xwrq
References
Other 5
- https://github.com/LemmyNet/lemmy/security/advisories/GHSA-h6hf-9846-xwrq
- https://github.com/LemmyNet/lemmy/releases/tag/0.19.18
- https://github.com/LemmyNet/lemmy/commit/9ffe586dafac1a46acf17edf90e0165e5503b2f1
- https://github.com/LemmyNet/lemmy
- https://join-lemmy.org/news/2026-04-20_-_Lemmy_Release_v0.19.18
More LemmyNet vulnerabilities
- TI-2026-23295 Lemmy: Unauthenticated SSRF via file_type query parameter injection in image endpoint CVSS 4.0HIGH 7.7
- TI-2026-26073 Lemmy's Activitypub-Federation has SSRF via 0.0.0.0 bypass in activitypub-federation-rust v4_is_invalid() CVSS 3.1MEDIUM 6.5
- TI-2026-39555 Lemmy: Stored XSS via markdown image alt-text in lemmy-ui html5-embed CVSS 4.0MEDIUM 6.4
- TI-2026-39552 Lemmy: Lower-ranked federated moderator can remove higher-ranked moderators CVSS 3.1MEDIUM 6.5
- TI-2026-39553 Lemmy: Blocked users can edit private messages sent before the block CVSS 4.0MEDIUM 5.3
- TI-2026-39554 Lemmy: `CollectionAdd::Featured` does not check the post is in the community CVSS 4.0MEDIUM 5.1
Sources
- CVE-2026-42181 · CVE Program
- CVE-2026-42181 · NVD
- FIRST EPSS
- GHSA-h6hf-9846-xwrq · GitHub Advisory Database · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences