musl libc before 1.2.7, when an untrusted regular expression is used with regcomp, has multiple integer overflows, possibly leading to…
Only affects musl 0.5.0 through 1.2.6 in applications that pass untrusted regular expressions to regcomp. Fixed in 1.2.7.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 1.2.7
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 1.2.7.
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 25/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Unclear
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
musl libc, the C standard library used by some Linux distributions, is affected by multiple integer overflows when it processes an untrusted regular expression passed to regcomp. An attacker who can supply such a pattern remotely, without logging in, could trigger incorrect memory allocation sizes and out-of-bounds heap writes, which could lead to code execution or crashes.
Read the original description
musl libc before 1.2.7, when an untrusted regular expression is used with regcomp, has multiple integer overflows, possibly leading to incorrect allocation sizes and out-of-bounds heap writes.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed, reachable over the network without a login · Unknown: Advisories don't say whether default setups are affected
- Reach?/20Unknown. No tracked technology or package matched
- Severity8.1/10CVSS 8.1
- No patch0/5No signal
What would change the score
- Would score about 70 if added to CISA KEV
- Would score about 65 if CISA's SSVC rates exploitation active
- Would score about 30 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 1.2.7.
Workaround: Prevent the processing of regular expressions from untrusted sources.
Timeline
- CVE published
- First seen by cve.now
- Record last updated
Affected versions
- musl -libc musl
From 0.5.0 · fixed in 1.2.7
Evidence 4
- Link
- Link
- Link
- Link
Corrections
None so far.
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Questions about CVE-2026-107891
Is CVE-2026-107891 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
Several integer overflows in musl's regcomp can be triggered by a crafted regular expression. The result is at least a denial-of-service crash that is predictable, and depending on the application and its heap use, arbitrary code execution may be possible.Source: openwall.com
Which versions are affected by CVE-2026-107891?
musl: from 0.5.0 before 1.2.7.Source: cve.now feed data
Am I affected, and how do I check?
Versions of musl from 0.5.0 through 1.2.6 are affected, and the bug needs an application that processes regular expressions from an untrusted source with the libc regcomp function. To check, look at the musl version installed on the system, and review whether the application passes user-supplied patterns to regcomp.Source: openwall.com
How do I fix CVE-2026-107891?
Upgrade musl to version 1.2.7, which contains the fix. Until the upgrade is applied, prevent the processing of regular expressions from untrusted sources.Source: openwall.com