CVE-2026-100355: Campfire vulnerable to SSRF via incomplete private-network denylist in the link-unfurl guard

What it is

Campfire is a web-based chat application. In version 1.4.4 and earlier, when a Campfire message contains a link, the server fetches it to build an OpenGraph unfurl preview. `RestrictedHTTP::PrivateNetworkGuard` relied on Ruby’s `IPAddr#private? `` IPAddr#loopback?`, and `IPAddr#link_local?` predicates plus IPv4-mapped and IPv4-compatible checks, which do not cover several special-use ranges. An authenticated user can post a link to a hostname resolving to CGNAT `100.64.0.0/10`, NAT64 `64:ff9b::/96` or `64:ff9b:1::/48`, or 6to4 `2002::/16` to bypass the guard and cause server-side requests to internal network resources. The NAT64 and 6to4 ranges can embed an internal IPv4 target. Confidentiality impact is limited to returned OpenGraph metadata, and most internal endpoints return none. There is no integrity or availability impact. An initial fix was released in version 1.4.5.

Description quoted from the CVE record (assigned by GitHub_M, published 2026-10-30).

Weakness: CWE-918: Server-Side Request Forgery (SSRF)

How it can be exploited

Exploitable over the network with high attack complexity needing low privileges and no user interaction. Impact: confidentiality low, integrity none, availability none. CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N

CISA assessment (SSVC): CISA has no evidence of exploitation. Automatable: no. Technical impact: partial.

Public exploit evidence (Exploit Observer)

Exploit Observer found 3 code repositories naming this CVE.

Code repositories that name a CVE are often scanners, copies or fakes, and some are malware. Read the code before running anything.

See all 4 references on Exploit Observer

Live scores

EPSS

0.003
low predicted chance of attack

VEDAS

0.987
strong exploit evidence

On CISA KEV

Not listed

Detection rule

Suricata

Who is affected

Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.

How to fix it

No fixed version or vendor advisory is listed in the CVE record yet. Watch the vendor’s security page.

How to detect it

Suricata rules (network detection)

1 rule that alert on traffic matching this exploit: VEDAS CVE-2026-100355 Campfire - SSRF Guard Bypass via Special-Use IP in Message. Add them to your Suricata rule set and reload.

alert http $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"VEDAS CVE-2026-100355 Campfire - SSRF Guard Bypass via Special-Use IP in Message"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"/messages"; nocase; fast_pattern; http.request_body; content:"message"; nocase; pcre:"/(?:100\.(?:6[4-9]|[7-9][0-9]|1[01][0-9]|12[0-7])\.|64(?:\x3a|%3a)ff9b(?:\x3a|%3a)|2002(?:\x3a|%3a))/i"; classtype:web-application-attack; reference:cve,CVE-2026-100355; reference:url,https://www.exploit.observer/?keyword=CVE-2026-100355&match=exact; reference:url,https://subdomain.center/?engine=ammonites&keyword=campfire&match=exact; sid:1104410; rev:1;)

CVE-2026-100355.rules on GitHub

References

Other references

• https://github.com/basecamp/once-campfire/security/advisories/GHSA-gjm7-g266-w3wj (x_refsource_CONFIRM)
• https://github.com/basecamp/once-campfire/pull/225 (x_refsource_MISC)
• https://github.com/basecamp/once-campfire/commit/69e8cd788593cf421c32626a5273c0b449ceee9b (x_refsource_MISC)
• https://github.com/basecamp/once-campfire/releases/tag/v1.4.5 (x_refsource_MISC)

Other databases

• CVE record (cve.org)
• NVD
• Exploit Observer

Where this comes from

This advisory is generated automatically by VEDAS from: CVE.org record, cve-scores (EPSS and VEDAS), Exploit Observer, vedas-signatures. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.