Vulnerability in Coturn
CVE-2026-27624
Coturn is a free open source implementation of TURN and STUN Server. Coturn is commonly configured to block loopback and internal ranges using "denied-peer-ip" and/or default loopback restrictions. CVE-2020-26262 addressed bypasses involving "0.0.0.0", "[::1]" and "[::]", but IPv4-mapped IPv6 is not covered. When sending a "CreatePermission" or "ChannelBind" request with the "XOR-PEER-ADDRESS" value of "::ffff:127.0.0.1", a successful response is received, even though "127.0.0.0/8" is blocked via "denied-peer-ip". The root cause is that, prior to the updated fix implemented in version 4.9.0, three functions in "src/client/ns_turn_ioaddr.c" do not check "IN6_IS_ADDR_V4MAPPED". "ioa_addr_is_loopback()" checks "127.x.x.x" (AF_INET) and "::1" (AF_INET6), but not "::ffff:127.0.0.1." "ioa_addr_is_zero()" checks "0.0.0.0" and "::", but not "::ffff:0.0.0.0." "addr_less_eq()" used by "ioa_addr_in_range()" for "denied-peer-ip" matching: when the range is AF_INET and the peer is AF_INET6, the comparison returns 0 without extracting the embedded IPv4. Version 4.9.0 contains an updated fix to address the bypass of the fix for CVE-2020-26262.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.2 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.005 (36.8th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 37th percentile — 36.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.005 · change: +0.002
Affected products
- Coturn — versions < 4.9.0
- Coturn Project
Weakness classification (CWE)
References
- github.com/coturn/coturn/security/advisories/GHSA-j8mm-mpf8-gvjg (Exploit, Vendor Advisory)
- github.com/coturn/coturn/security/advisories/GHSA-6g6j-r9rf-cm7p (Not Applicable)
- github.com/coturn/coturn/commit/b80eb898ba26552600770162c26a8ae7f3661b0b (Patch)
Frequently asked questions
- What is CVE-2026-27624?
- CVE-2026-27624 is a high-severity vulnerability in Coturn, classified under Improper Access Control. CVSS score: 7.2/10. Published 2026-02-25.
- How severe is CVE-2026-27624?
- High severity. CVSS v3 base score is 7.2 out of 10.