CVE-2020-11958: re2c 1.3 has a heap-based buffer overflow in Scanner::fill in parse/scanner.cc via a long lexeme.

This month

HIGH 7.8WATCHLISTDOWNGRADEMITIGATE

CVE-2020-11958 is a high-severity flaw (CVSS 7.8) affecting re2c, ubuntu linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

re2c 1.3 has a heap-based buffer overflow in Scanner::fill in parse/scanner.cc via a long lexeme.

Why this priority

High severity
On your watchlist

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

Risk facts

CVSS score	7.8 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	1.7% (top 23%)
CISA exploited list	No
Weakness	CWE-787
Published	2020-04-21
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: canonical · re2c

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

Am I affected?

Timeline

2020-04-21 01:15 UTCPublished CVE record published
2026-06-17 02:51 UTCUpdated Record last modified

re2c re2c DOWNGRADE

Affected: 1.3

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.3

1. Check installed version

apt-cache policy re2c || rpm -q re2c || re2c --version

2. No fixed release: DOWNGRADE to a release before 1.3 (Debian / Ubuntu)

apt-cache madison re2c sudo apt install re2c=<VERSION_BEFORE_1.3> sudo apt-mark hold re2c

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

dnf --showduplicates list re2c sudo dnf downgrade re2c-<VERSION_BEFORE_1.3> sudo dnf versionlock add re2c

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.

canonical ubuntu linux MITIGATE

Affected: 19.10 · 20.04

Fixed in: no fixed release known

Safe to downgrade to: a release before 19.10

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-2020-11958?

re2c: downgrade or apply the listed mitigation; ubuntu linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-11958 being exploited?

CVE-2020-11958 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-2020-11958 affect?

CVE-2020-11958 affects re2c, ubuntu linux. Severity is high (CVSS 7.8). re2c 1.3 has a heap-based buffer overflow in Scanner::fill in parse/scanner.cc via a long lexeme.

How urgent is CVE-2020-11958?

Priority 52/100. High severity; On your watchlist

Software pages

Ubuntu vulnerabilities

Related CVEs

CVE-2022-23901 CRITICAL 9.8 DOWNGRADE A stack overflow re2c 2.2 exists due to infinite recursion issues in src/dfa/dead_rules.cc.
CVE-2018-21232 MEDIUM 5.5 UPGRADE re2c before 2.0 has uncontrolled recursion that causes stack consumption in find_fixed_tags.

References

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