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CVE-2026-55735: Improper Verification of Cryptographic Signature in ueberauth guardian allows an unauthenticated attacker to r

46
This week
HIGH 7.5REMOTEUPGRADE

CVE-2026-55735 is a high-severity flaw (CVSS 7.5) affecting guardian. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Improper Verification of Cryptographic Signature in ueberauth guardian allows an unauthenticated attacker to revoke a victim's session with a forged token. Guardian.revoke/3 in lib/guardian.ex decodes the supplied token with peek/1, which performs no signature verification (it only base64-decodes the JWT header and payload). The resulting unverified claims are forwarded directly to the configured token module's revoke callback and the implementa

Why this priority

  • High severity
  • Public exploit reference
  • Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score7.5 (High)
Attack vectorNetwork (remote)
Attack complexityLow
Privileges neededNone
User interactionNone
EPSS exploit chance0.5% (top 61%)
CISA exploited listNo
WeaknessCWE-347
Published2026-08-01
Last modified2026-10-23
Publisher (CNA): EEF · Vendor: ueberauth

Last updated 2026-10-23 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

ueberauth guardian UPGRADE
Affected: >= 1.0.0 and < 2.4.1
Fixed in: 2.4.1
Safe to downgrade to: a release before 1.0.0
1. Check installed version
apt-cache policy guardian || rpm -q guardian || guardian --version
2. UPGRADE to 2.4.1 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade guardian
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade guardian
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
3. If no update is available yet, DOWNGRADE to a release before 1.0.0 (Debian / Ubuntu)
apt-cache madison guardian sudo apt install guardian=<VERSION_BEFORE_1.0.0> sudo apt-mark hold guardian
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list guardian sudo dnf downgrade guardian-<VERSION_BEFORE_1.0.0> sudo dnf versionlock add guardian
Downgrade risk
Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.
After downgrade
Restart the service, and keep the package held until a fixed release ships.

Exact fixes by distribution

Fedora 46 · rubygem-eventmachine · FIXED · 1.2.7-37.fc46 · FEDORA-2026-7194c202a2 · source
sudo dnf upgrade --advisory=FEDORA-2026-7194c202a2

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-55735?

guardian: upgrade to 2.4.1. Exact commands for each OS are on this page.

Is CVE-2026-55735 being exploited?

CVE-2026-55735 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-55735 affect?

CVE-2026-55735 affects guardian. Severity is high (CVSS 7.5). Improper Verification of Cryptographic Signature in ueberauth guardian allows an unauthenticated attacker to revoke a victim's session with a forged token. Guardian.revoke/3 in lib/guardian.ex decodes the supplied token with peek/1, which

How urgent is CVE-2026-55735?

Priority 46/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

References

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