CVE-2021-3826: Heap/stack buffer overflow in the dlang_lname function in d-demangle.c in libiberty allows attackers to potent

This month

MEDIUM 6.5DOWNGRADEMITIGATE

CVE-2021-3826 is a medium-severity flaw (CVSS 6.5) affecting gcc, fedora. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Heap/stack buffer overflow in the dlang_lname function in d-demangle.c in libiberty allows attackers to potentially cause a denial of service (segmentation fault and crash) via a crafted mangled symbol.

Why this priority

No elevated risk signals yet

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	1.5% (top 26%)
CISA exploited list	No
Weakness	CWE-119, CWE-787
Published	2022-09-01
Last modified	2026-10-14

Publisher (CNA): Red Hat, Inc. · Vendor: fedoraproject · gnu

Last updated 2026-10-14 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2022-09-01 21:15 UTCPublished CVE record published
2026-10-14 10:17 UTCUpdated Record last modified

gnu gcc DOWNGRADE

Affected: 11.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 11.2

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 11.2 (Debian / Ubuntu)

apt-cache madison gcc sudo apt install gcc=<VERSION_BEFORE_11.2> sudo apt-mark hold gcc

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list gcc sudo dnf downgrade gcc-<VERSION_BEFORE_11.2> sudo dnf versionlock add gcc

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.

fedoraproject fedora MITIGATE

Affected: 35 · 36 · 37

Fixed in: no fixed release known

Safe to downgrade to: a release before 35

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

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-2021-3826?

gcc: downgrade or apply the listed mitigation; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-3826 being exploited?

CVE-2021-3826 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-2021-3826 affect?

CVE-2021-3826 affects gcc, fedora. Severity is medium (CVSS 6.5). Heap/stack buffer overflow in the dlang_lname function in d-demangle.c in libiberty allows attackers to potentially cause a denial of service (segmentation fault and crash) via a crafted mangled symbol.

How urgent is CVE-2021-3826?

Priority 41/100. No elevated risk signals yet.

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CVE-2019-15847 HIGH 7.5 UPGRADE MITIGATE The POWER9 backend in GNU Compiler Collection (GCC) before version 10 could optimize multiple calls of the __b
CVE-2018-12886 HIGH 8.1 UPGRADE stack_protect_prologue in cfgexpand.c and stack_protect_epilogue in function.c in GNU Compiler Collection (GCC

References

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