GNU libidn2 before 2.2.0 fails to perform the roundtrip checks specified in RFC3490 Section 4.2 when converting A-labels to U-labels.
GNU libidn2 before 2.2.0 fails to perform the roundtrip checks specified in RFC3490 Section 4.2 when converting A-labels to U-labels. This makes it possible in some circumstances for one domain to impersonate another. By creating a malicious domain that matches a target domain except for the inclusion of certain punycoded Unicode characters (that would be discarded when converted first to a Unicode label and then back to an ASCII label), arbitrary domains can be impersonated.
- Published
- Oct 22, 2019
- Updated
- Jun 16, 2026
- EPSS
- 3.0% · 87th percentile
- CWE
- CWE-20
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Report tools
Action score
31
Monitor
Low priority for now.
- CVSS
- 30 / 40 · 7.5 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 1 / 30 · 3.0%
Noroxi analysis
No Noroxi analysis for this record yet
We don't hand-write analysis for the hundreds of thousands of vulnerabilities in the database; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.
We use this product, ask for helpAffected systems
| Vendor | Product | CPE |
|---|---|---|
| gnu | libidn2 | cpe:2.3:a:gnu:libidn2 |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- gnu libidn2before 2.2.0
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Alpine:v3.12 | libidn2 | before 2.2.0-r0 | 2.2.0-r0 |
| Debian:12 | libidn2 | before 2.2.0-1 | 2.2.0-1 |
| openSUSE:Leap 15.0 | libidn2 | before 2.2.0-lp150.2.3.1 | 2.2.0-lp150.2.3.1 |
| openSUSE:Leap 15.1 | libidn2 | before 2.2.0-lp151.3.3.1 | 2.2.0-lp151.3.3.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 | libidn2 | before 2.2.0-3.3.1 | 2.2.0-3.3.1 |
Same product
gnu: all recordsOther highest-scoring records for the same primary product.
- CVE-2019-18224idn2_to_ascii_4i in lib/lookup.c in GNU libidn2 before 2.1.1 has a heap-based buffer overflow via a long domain string.40Plan
- CVE-2017-14062Integer overflow in the decode_digit function in puny_decode.c in Libidn2 before 2.0.4 allows remote attackers to cause a denial of service 40Plan
- CVE-2017-14061Integer overflow in the _isBidi function in bidi.c in Libidn2 before 2.0.4 allows remote attackers to cause a denial of service or possibly 40Plan
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| alpine:libidn2 | 2.2.0-r0 · Alpine:v3.12 | Package registry (OSV) |
| debian:libidn2 | 2.2.0-1 · Debian:12 | Package registry (OSV) |
| opensuse:libidn2 | 2.2.0-lp151.3.3.1 · openSUSE:Leap 15.1 | Package registry (OSV) |
| suse:libidn2 | 2.2.0-3.3.1 · SUSE:Linux Enterprise Module for Basesystem 15 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- none
- Integrity
- high · data or configuration can be modified
- Availability
- none
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- High
- Availability impact
- None
Weakness class (CWE)
CWE-20 · Improper Input ValidationCVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
- Buffer Overflow via Environment VariablesCAPEC-10likelihood: High · High
- Server Side Include (SSI) InjectionCAPEC-101likelihood: High · High
- Cross Zone ScriptingCAPEC-104likelihood: Medium · High
- Command Line Execution through SQL InjectionCAPEC-108likelihood: Low · Very High
- Object Relational Mapping InjectionCAPEC-109likelihood: Low · High
- SQL Injection through SOAP Parameter TamperingCAPEC-110likelihood: High · Very High
- Double EncodingCAPEC-120likelihood: Low · Medium
- Subverting Environment Variable ValuesCAPEC-13likelihood: High · Very High
ATT&CK techniques
- Obfuscated Files or InformationT1027
- Masquerading: Invalid Code SignatureT1036.001
- Steal Web Session CookieT1539
- Subvert Trust Controls: Code SigningT1553.002
- Impair Defenses:Impair Command History LoggingT1562.003
- Hijack Execution Flow:Dynamic Linker HijackingT1574.006
- Hijack Execution Flow:Path Interception by PATH Environment VariableT1574.007
Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
- lists.opensuse.org/opensuse-security-announce/2019-12/msg00008.html
- lists.opensuse.org/opensuse-security-announce/2019-12/msg00009.html
- gitlab.com/libidn/libidn2/commit/241e8f486134793cb0f4a5b0e5817a97883401f5
- gitlab.com/libidn/libidn2/commit/614117ef6e4c60e1950d742e3edf0a0ef8d389de
- gitlab.com/libidn/libidn2/merge_requests/71
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3UFT76Y7OSGPZV3EBEHD6ISVUM3DLARM/
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/KXDKYWFV6N2HHVSE67FFDM7G3FEL2ZNE/
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ONG3GJRRJO35COPGVJXXSZLU4J5Y42AT/
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RSI4TI2JTQWQ3YEUX5X36GTVGKO4QKZ5/
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/U6ZXL2RDNQRAHCMKWPOMJFKYJ344X4HL/
- security.gentoo.org/glsa/202003-63
- usn.ubuntu.com/4168-1/
Vendor advisories and official records. Exploit/PoC links are deliberately left out.