CVE-2026-6291: Bleichenbacher padding oracle in PKCS#7 KTRI decryption

Routine

MEDIUM 6.5UPGRADE

CVE-2026-6291 is a medium-severity flaw (CVSS 6.5) affecting wolfssl. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Bleichenbacher padding oracle in PKCS#7 KTRI decryption. When decrypting PKCS#7 EnvelopedData using RSA PKCS#1 v1.5 key transport, wolfSSL returned distinguishable error codes depending on whether RSA padding validation failed versus whether the decrypted content was malformed. An attacker able to submit crafted EnvelopedData messages and observe error responses could use this as a padding oracle to incrementally recover the encrypted Content Enc

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.2% (top 85%)
CISA exploited list	No
Weakness	CWE-208
Published	2026-06-25
Last modified	2026-06-26

Publisher (CNA): wolfSSL Inc. · Vendor: wolfssl

Last updated 2026-06-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-25 18:16 UTCPublished CVE record published
2026-06-26 16:51 UTCUpdated Record last modified

wolfssl wolfssl UPGRADE

Affected: >= 3.9.10 and < 5.9.2

Fixed in: 5.9.2

Safe to downgrade to: a release before 3.9.10

1. Check installed version

apt-cache policy wolfssl || rpm -q wolfssl || wolfssl --version

2. UPGRADE to 5.9.2 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade wolfssl

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade wolfssl

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 3.9.10 (Debian / Ubuntu)

apt-cache madison wolfssl sudo apt install wolfssl=<VERSION_BEFORE_3.9.10> sudo apt-mark hold wolfssl

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list wolfssl sudo dnf downgrade wolfssl-<VERSION_BEFORE_3.9.10> sudo dnf versionlock add wolfssl

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.

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-2026-6291?

wolfssl: upgrade to 5.9.2. Exact commands for each OS are on this page.

Is CVE-2026-6291 being exploited?

CVE-2026-6291 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-2026-6291 affect?

CVE-2026-6291 affects wolfssl. Severity is medium (CVSS 6.5). Bleichenbacher padding oracle in PKCS#7 KTRI decryption. When decrypting PKCS#7 EnvelopedData using RSA PKCS#1 v1.5 key transport, wolfSSL returned distinguishable error codes depending on whether RSA padding validation failed versus whethe

How urgent is CVE-2026-6291?

Priority 27/100. No elevated risk signals yet.

Software pages

wolfSSL vulnerabilities

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References

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