CVE-2026-21620 — TFTP Path Traversal
Relative Path Traversal, Improper Isolation or Compartmentalization vulnerability in erlang otp erlang/otp (tftp_file modules), erlang otp inets (tftp_file modules), erlang otp tftp (tftp_file modules) allows Relative Path Traversal. This vulnerability is associated with program files lib/tftp/src/tftp_file.erl, src/tftp_file.erl. This issue affects OTP from OTP 17.0 before OTP 28.3.2, OTP 27.3.4.8 and OTP 26.2.5.17, corresponding to tftp from 1.0 before 1.2.4, 1.2.2.1 and 1.1.1.1; also inets from 5.10 before 7.0.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.5% (30-day exploitation probability)+6
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Erlang Erlang/otp).
- No fix documented in the sources: reduce exposure and monitor the vendor advisory.
- Search available logs for exploit probes matching the vulnerability class (file handling), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Erlang | Erlang/otp | ≥ 17.0≥ 07b8f441ca711f9812fad9e9115bab3c3aa92f79≥ 5.10 and < 7.0≥ 1.0 | Vulnerable | CVE Program (cve.org) e CISA ADP |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 2.3 | CVSS 4.0 | Low | — | — | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db via NIST National Vulnerability Database |
| 2.3 | CVSS 4.0 | Low | — | — | EEF via CVE Program (cve.org) e CISA ADP |
CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:L/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 (score shown at the top: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
EPSS over time FIRST
Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.49%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
- Monitor file creation in web directories and paths with traversal sequences (../).
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · erlang/otp
- SSVC assessment updated
- Record published
- CVSS changed · 2.3
- Source status changed · → Deferred
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× Official description updated · Oct 13, 2026 – Oct 13, 2026
References
8 on the record
- github.com/erlang/otp/commit/655fb95725ba2fb811740b57e106873833824344
- github.com/erlang/otp/commit/3970738f687325138eb75f798054fa8960ac354e
- github.com/erlang/otp/pull/10706
- github.com/erlang/otp/commit/696fdec922661d4a3cc528fc34bc24fae8d4ad8a
- osv.dev/vulnerability/EEF-CVE-2026-21620
- cna.erlef.org/cves/CVE-2026-21620.html
- www.erlang.org/doc/system/versions.html
- github.com/erlang/otp/security/advisories/GHSA-hmrc-prh3-rpvp
Elsewhere on this site
Related CVEs (same products)
- Medium CVE-2026-96596 erl_tar:extract/2 loops forever on a GNU sparse member with a trailing hole 1d
- High CVE-2026-94200 TLS 1.3 client ticket store crashed by NewSessionTicket with empty early_data extension in ssl 1d
- Medium CVE-2026-105236 TLS 1.2 session resumption in ssl crosses SNI virtual-host client-certificate trust boundaries 1d
- High CVE-2026-59250 Megaco flex scanner buffer overflow via oversized property parm name Jul 27, 2026
- High CVE-2026-59251 Denial of service via exponential certificate policy tree growth in path validation Jul 27, 2026
- High CVE-2026-58227 TLS/DTLS denial of service via unbounded recursion on cross-signed peer certificate chain Jul 27, 2026
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No fixed version, patch or mitigation documented.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-21620 is "TFTP Path Traversal", rated Low. It affects Erlang/otp (Erlang); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 2.3 describes technical severity. EPSS 0.49% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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