Actual Sync Server: CORS Proxy GitHub API Allowlist Prefix Bypass Leaks Private Repositories Through the Server GitHub Token

published 2026-09-25 44 d ago modified 2026-10-07 32 d ago also GHSA-m62c-5q34-f3cf , EUVD-2026-87369

cvss: 7.1; version 4.0, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 17%
public exploits: 0; none known

Actual is a local-first personal finance tool. Prior to 26.7.0, Actual Sync Server's CORS proxy is intended to let authenticated users fetch resources only from repositories listed in the official plugin allowlist. When `ACTUAL_GITHUB_TOKEN` is configured, the proxy automatically attaches the server's GitHub token to GitHub requests. The GitHub API allowlist check uses a raw `startsWith()` prefix test for `/repos/{owner}/{repo}` without requiring a path boundary after the repository name. If an allowlisted public plugin repository is `https://github.com/acme/plugin`, the proxy also accepts GitHub API URLs. Those URLs are outside the allowlisted repository but still pass because their API path starts with `/repos/acme/plugin`. The proxy then forwards the request with the server's `ACTUAL_GITHUB_TOKEN`, allowing any authenticated Actual user to read private GitHub resources reachable by that token. Version 26.7.0 fixes the issue.

Patch / fix

fixed in 1

npm @actual-app/sync-server 26.7.0

CISA SSVC

Exploitation: Proof of concept is public
Automatable: no
Technical impact: partial
Assessed: 41 d ago (2026-09-28)

Exploit prediction

0.26% chance of exploitation in the next 30 days, higher than 17% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/actualbudget/actual/security/advisories/GHSA-m62c-5q34-f3cf referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	4.0	7.1	CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
CNA	4.0	7.1	CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected packages

ecosystem	package	affected	fixed in
npm	@actual-app/sync-server	<26.7.0	26.7.0

Affected products

actualbudget actual

Classification

Weakness

CWE-200 Exposure of Sensitive Information to an Unauthorized Actor
CWE-284 Improper Access Control
CWE-863 Incorrect Authorization

References

github.com /actualbudget/actual/security/advisories/GHSA-m62c-5q34-f3cf
exploit, web
nvd.nist.gov /vuln/detail/CVE-2026-57449
advisory
github.com /actualbudget/actual
package

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.

Summary