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Fencer Vulns
medium 5.8

CVE-2026-55430 json

Coder's subdomain workspace app routing trusts unauthenticated X-Forwarded-Host header, enabling cross-app data access

published 2026-07-06 4 mo ago modified 2026-07-08 4 mo ago also GHSA-5g4w-3vw9-478w , GO-2026-5917 , EUVD-2026-42136

cvss
5.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 11%
public exploits
0
none known

Summary

Coder allows organizations to provision remote development environments via Terraform. Prior to versions 2.29.7, 2.32.7, 2.33.8, and 2.34.2, the workspace app proxy resolves the target app from `httpapi.RequestHost()` which prefers the `X-Forwarded-Host` header over the real `Host` header. No middleware strips `X-Forwarded-Host` before routing and the header is not browser-forbidden so client-side JavaScript can set it on `fetch()` calls. Practical exploitation requires subdomain app routing (wildcard hostname) enabled, a victim who visits the attacker's shared app and a deployment whose upstream proxy does not strip `X-Forwarded-Host`. The fix in versions 2.29.7, 2.32.7, 2.33.8, and 2.34.2 trusts `X-Forwarded-Host` only from configured trusted proxies and otherwise resolves the routing host from the verified request host. As a workaround, place an upstream reverse proxy that strips or overwrites `X-Forwarded-Host` on untrusted requests.

Patch / fix

  • go github.com/coder/coder/v2 2.29.17, 2.32.7, 2.33.8, 2.34.2
  • coder coder 2.29.17, 2.32.7, 2.33.8, 2.34.2
  • govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1

opensuse advisories openSUSE-SU-2026:21483-1

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
4 mo ago

Exploit prediction

0.21% chance of exploitation in the next 30 days, higher than 11% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.8 CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:N/A:N
NVD 3.1 6.8 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:N/A:N
GitHub 3.1 5.8 CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
go github.com/coder/coder/v2
>=2.34.0, <2.34.2
>=2.33.0, <2.33.8
>=2.30.0, <2.32.7
<2.29.17
2.34.2
2.33.8
2.32.7
2.29.17
go github.com/coder/coder
all versions
 no fix listed

Affected products

  • coder coder

Classification

Weakness
  • CWE-345 Insufficient Verification of Data Authenticity
  • CWE-441 Unintended Proxy or Intermediary

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.