CVE-2026-50722· NVD / CVE Program· CNA libreswan

IKEv2 Denial of Service via RSA-SHA1 (PKCS#1 RSASSA-PKCS1-v1_5) authentication payload

Noroxi assessment

Priority: Monitor (action score 23/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.34% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
According to CISA the attack is automatable: targets can be found by mass scanning.
Fixed version: azl3 libreswan 4.15-1 on Azure Linux 3.0 4.15-2.

Low priority for now. Upgrade to azl3 libreswan 4.15-1 on Azure Linux 3.0 4.15-2 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Libreswan, via the function RSA_authenticate_hash_signature_pkcs1_1_5_rsa(), did not correctly verify the DER encoding of the ASN.1 digest when the IKEv2 AUTH payload was encoded using RSASSA-PKCS1-v1_5 (RFC 8017). A remote attacker can use a variation on the Bleichenbacher attack to forge the AUTH payload when small public exponents are used (e.g., e=3), leading to impersonation. Additionally, a remote attacker, by encoding a shorter than expected hash in the AUTH payload, could trigger an assertion leading to denial-of-service. The daemon aborts and restarts; continued exploitation causes sustained denial of service. Remote code execution is not possible. X.509 certificate verifications of the remote IKE peer are not affected.

MediumCVSS 5.9 · v3.1—No exploit Fix available

Published: Jul 2, 2026
Updated: Jul 9, 2026
EPSS: 0.3% · 26th percentile
CWE: CWE-347

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 23 / 40 · 5.9 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.3%

CISA SSVC decision

Exploitation: none
Automatable: yes
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 5.9
CNA · libreswan: 7.5; 1.6 point gap

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
libreswan	libreswan	cpe:2.3:a:libreswan:libreswan

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

libreswan libreswanbefore 5.3.1

Versions reported by the vendor

Affected version ranges reported by the assigning authority (libreswan). Independent of NVD's CPE analysis and usually ahead of it.

The Libreswan Project libreswan
- 5.3.1not affected
- up to and including 5.3affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
AlmaLinux:10	libreswan	before 5.3.2-1.el10_2	5.3.2-1.el10_2
AlmaLinux:10	libreswan-minimal	before 5.3.2-1.el10_2	5.3.2-1.el10_2
AlmaLinux:8	libreswan	before 4.12-2.el8_10.6	4.12-2.el8_10.6
AlmaLinux:9	libreswan	before 4.15-10.el9_8	4.15-10.el9_8
Debian:12	libreswan	all versions	—
Debian:14	libreswan	before 5.2-2.5	5.2-2.5
Red Hat:enterprise_linux_eus:10.0	libreswan	before 0:5.2-1.el10_0.5	0:5.2-1.el10_0.5
Red Hat:enterprise_linux:10.2	libreswan	before 0:5.3.2-1.el10_2	0:5.3.2-1.el10_2
Red Hat:enterprise_linux:10.2	libreswan-debugsource	before 0:5.3.2-1.el10_2	0:5.3.2-1.el10_2
Red Hat:enterprise_linux:10.2	libreswan-minimal	before 0:5.3.2-1.el10_2	0:5.3.2-1.el10_2
Red Hat:enterprise_linux:10.2	libreswan-minimal-debuginfo	before 0:5.3.2-1.el10_2	0:5.3.2-1.el10_2
Red Hat:enterprise_linux:8::appstream	libreswan	before 0:4.12-2.el8_10.6	0:4.12-2.el8_10.6
Red Hat:enterprise_linux:8::appstream	libreswan-debuginfo	before 0:4.12-2.el8_10.6	0:4.12-2.el8_10.6
Red Hat:enterprise_linux:8::appstream	libreswan-debugsource	before 0:4.12-2.el8_10.6	0:4.12-2.el8_10.6
Red Hat:enterprise_linux:9::appstream	libreswan	before 0:4.15-10.el9_8	0:4.15-10.el9_8
Red Hat:enterprise_linux:9::appstream	libreswan-debuginfo	before 0:4.15-10.el9_8	0:4.15-10.el9_8
Red Hat:enterprise_linux:9::appstream	libreswan-debugsource	before 0:4.15-10.el9_8	0:4.15-10.el9_8
Red Hat:enterprise_linux:9::fastdatapath	libreswan	before 0:5.3.2-1.el9fdp	0:5.3.2-1.el9fdp
Red Hat:enterprise_linux:9::fastdatapath	libreswan-debuginfo	before 0:5.3.2-1.el9fdp	0:5.3.2-1.el9fdp
Red Hat:enterprise_linux:9::fastdatapath	libreswan-debugsource	before 0:5.3.2-1.el9fdp	0:5.3.2-1.el9fdp
Red Hat:rhel_e4s:8.8::appstream	libreswan	before 0:4.9-3.el8_8.3	0:4.9-3.el8_8.3
Red Hat:rhel_e4s:9.2::appstream	libreswan	before 0:4.9-5.el9_2.5	0:4.9-5.el9_2.5
Red Hat:rhel_e4s:9.4::appstream	libreswan	before 0:4.12-3.el9_4.2	0:4.12-3.el9_4.2
Red Hat:rhel_eus:9.6::appstream	libreswan	before 0:4.15-8.el9_6.1	0:4.15-8.el9_6.1

Same product

libreswan: all records

Other highest-scoring records for the same primary product.

CVE-2013-7283Race condition in the libreswan.spec files for Red Hat Enterprise Linux (RHEL) and Fedora packages in libreswan 3.6 has unspecified impact a
37Monitor
CVE-2022-23094Libreswan 4.2 through 4.5 allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a crafted IKE
31Monitor
CVE-2020-1763An out-of-bounds buffer read flaw was found in the pluto daemon of libreswan from versions 3.27 till 3.31 where, an unauthenticated attacker
31Monitor
CVE-2019-12312In Libreswan 3.27 an assertion failure can lead to a pluto IKE daemon restart.
31Monitor
CVE-2016-5391libreswan before 3.18 allows remote attackers to cause a denial of service (NULL pointer dereference and pluto daemon restart).
31Monitor
CVE-2016-5361programs/pluto/ikev1.c in libreswan before 3.17 retransmits in initial-responder states, which allows remote attackers to cause a denial of
31Monitor

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
azl3 libreswan 4.15-1 on Azure Linux 3.0	4.15-2 · CBL-Mariner Releases	Microsoft (MSRC)
almalinux:libreswan	4.12-2.el8_10.6 · AlmaLinux:8	Package registry (OSV)
almalinux:libreswan-minimal	5.3.2-1.el10_2 · AlmaLinux:10	Package registry (OSV)
debian:libreswan	5.2-2.5 · Debian:14	Package registry (OSV)
red hat:libreswan	0:4.12-2.el8_10.6 · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
red hat:libreswan-debuginfo	0:4.12-2.el8_10.6 · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
red hat:libreswan-debugsource	0:4.12-2.el8_10.6 · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
red hat:libreswan-minimal	0:5.3.2-1.el10_2 · Red Hat:enterprise_linux:10.2	Package registry (OSV)
red hat:libreswan-minimal-debuginfo	0:5.3.2-1.el10_2 · Red Hat:enterprise_linux:10.2	Package registry (OSV)
rocky linux:libreswan	0:4.12-2.el8_10.6 · Rocky Linux:8	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.

EPSS, last 120 days

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.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Yeonghyeon Choifinder
Duyeong Kimfinder
Andrew Cagney (The Libreswan Team)analyst

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

CVE-2026-507210 days apartIKEv1 Denial of Service via RSA-SHA1 (PKCS#1 Version 1.5 Encrypted) authentication payload
23Monitor

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.
Special conditions such as timing or configuration are required.

If successful

Confidentiality: none
Integrity: none
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: High
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: None
Availability impact: High

Weakness class (CWE)

CWE-347 · Improper Verification of Cryptographic Signature

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

nvd-primary

Root cause

The verifier takes the algorithm to verify with from the token’s own header. Untrusted data ends up deciding its own verification rule.

The bug in code

The whole CWE-347 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1const claims = jwt.verify(token, publicKey);

Fixed

1const claims = jwt.verify(token, publicKey, {2  algorithms: ["RS256"],3  issuer: "https://id.example.com",4  audience: "portal",5});

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)

ATT&CK techniques

—

Change log

Fix✗ → ✓Sep 28, 2026, 10:44 PM UTC

For records you follow, these changes also arrive as notifications. →

References

libreswan.org/security/CVE-2026-50721/CVE-2026-50721.txt

Show all references (3 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records