CVE-2021-35525: PostSRSd before 1.11 allows a denial of service (subprocess hang) if Postfix sends certain long data fields su

Q: How do I fix CVE-2021-35525?

postsrsd: upgrade to 1.11. Exact commands for each OS are on this page.

Q: Is CVE-2021-35525 being exploited?

CVE-2021-35525 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-35525 affect?

CVE-2021-35525 affects postsrsd. Severity is medium (CVSS 5.3). PostSRSd before 1.11 allows a denial of service (subprocess hang) if Postfix sends certain long data fields such as multiple concatenated email addresses. NOTE: the PostSRSd maintainer acknowledges "theoretically, this error should never oc

Q: How urgent is CVE-2021-35525?

Priority 43/100. Remotely exploitable, no login, no user action

This month

MEDIUM 5.3REMOTEUPGRADE

CVE-2021-35525 is a medium-severity flaw (CVSS 5.3) affecting postsrsd. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

PostSRSd before 1.11 allows a denial of service (subprocess hang) if Postfix sends certain long data fields such as multiple concatenated email addresses. NOTE: the PostSRSd maintainer acknowledges "theoretically, this error should never occur ... I'm not sure if there's a reliable way to trigger this condition by an external attacker, but it is a security bug in PostSRSd nevertheless."

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.7% (top 23%)
CISA exploited list	No
Published	2021-06-28
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: postsrsd project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-06-28 18:15 UTCPublished CVE record published
2026-06-17 03:57 UTCUpdated Record last modified

postsrsd project postsrsd UPGRADE

Affected: < 1.11

Fixed in: 1.11

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 1.11 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade postsrsd

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

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-2021-35525?

postsrsd: upgrade to 1.11. Exact commands for each OS are on this page.

Is CVE-2021-35525 being exploited?

CVE-2021-35525 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-2021-35525 affect?

CVE-2021-35525 affects postsrsd. Severity is medium (CVSS 5.3). PostSRSd before 1.11 allows a denial of service (subprocess hang) if Postfix sends certain long data fields such as multiple concatenated email addresses. NOTE: the PostSRSd maintainer acknowledges "theoretically, this error should never oc

How urgent is CVE-2021-35525?

Priority 43/100. Remotely exploitable, no login, no user action

Software pages

Postfix vulnerabilities

Related CVEs

CVE-2020-35573 HIGH 7.5 UPGRADE MITIGATE srs2.c in PostSRSd before 1.10 allows remote attackers to cause a denial of service (CPU consumption) via a lo

References

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