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CVE-2026-77299

Regexp2: Unbounded memory amplification via large `{m}` quantifier on a zero-width subexpression

7.5 High

Regexp2 is a feature-rich RegExp engine for Go. Prior to version 2.3.0, when regexp2 compiles and matches a pattern containing a large fixed-count quantifier applied to a zero-width subexpression — e.g. (?:){50000000} — the match engine executes the empty loop body m-1 times, pushing two integers onto the backtracking stack on every iteration. Because the parser accepts any repetition count up to math.MaxInt32 and the backtracking stack grows without bound, a pattern of fewer than 20 bytes matched against an empty input can force multi-gigabyte allocation and OOM-kill the process. MatchTimeout does not fully mitigate this because the memory is allocated faster than the 100 ms timeout clock can fire. This issue has been patched in version 2.3.0.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
High

Exploit likelihood

0.35%Unchanged since Nov 6, 2026
90%50%10%1%

What each source reports

CVE List Score used 7.5

Regexp2: Unbounded memory amplification via large `{m}` quantifier on a zero-width subexpression

Regexp2 is a feature-rich RegExp engine for Go. Prior to version 2.3.0, when regexp2 compiles and matches a pattern containing a large fixed-count quantifier applied to a zero-width subexpression — e.g. (?:){50000000} — the match engine executes the empty loop body m-1 times, pushing two integers onto the backtracking stack on every iteration. Because the parser accepts any repetition count up to math.MaxInt32 and the backtracking stack grows without bound, a pattern of fewer than 20 bytes matched against an empty input can force multi-gigabyte allocation and OOM-kill the process. MatchTimeout does not fully mitigate this because the memory is allocated faster than the 100 ms timeout clock can fire. This issue has been patched in version 2.3.0.

Record
CVE-2026-77299
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-400, CWE-770
Updated
2026-11-06
EUVDEUVD-2026-117884 7.5

Regexp2 is a feature-rich RegExp engine for Go. Prior to version 2.3.0, when regexp2 compiles and matches a pattern containing a large fixed-count quantifier applied to a zero-width subexpression — e.g. (?:){50000000} — the match engine executes the empty loop body m-1 times, pushing two integers onto the backtracking stack on every iteration. Because the parser accepts any repetition count up to math.MaxInt32 and the backtracking stack grows without bound, a pattern of fewer than 20 bytes matched against an empty input can force multi-gigabyte allocation and OOM-kill the process. MatchTimeout does not fully mitigate this because the memory is allocated faster than the 100 ms timeout clock can fire. This issue has been patched in version 2.3.0.

Record
EUVD-2026-117884
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-06
NVD 7.5

Regexp2 is a feature-rich RegExp engine for Go. Prior to version 2.3.0, when regexp2 compiles and matches a pattern containing a large fixed-count quantifier applied to a zero-width subexpression — e.g. (?:){50000000} — the match engine executes the empty loop body m-1 times, pushing two integers onto the backtracking stack on every iteration. Because the parser accepts any repetition count up to math.MaxInt32 and the backtracking stack grows without bound, a pattern of fewer than 20 bytes matched against an empty input can force multi-gigabyte allocation and OOM-kill the process. MatchTimeout does not fully mitigate this because the memory is allocated faster than the 100 ms timeout clock can fire. This issue has been patched in version 2.3.0.

Record
CVE-2026-77299
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-400, CWE-770
Updated
2026-11-06
OSV 7.5

Regexp2: Unbounded memory amplification via large `{m}` quantifier on a zero-width subexpression

Regexp2 is a feature-rich RegExp engine for Go. Prior to version 2.3.0, when regexp2 compiles and matches a pattern containing a large fixed-count quantifier applied to a zero-width subexpression — e.g. (?:){50000000} — the match engine executes the empty loop body m-1 times, pushing two integers onto the backtracking stack on every iteration. Because the parser accepts any repetition count up to math.MaxInt32 and the backtracking stack grows without bound, a pattern of fewer than 20 bytes matched against an empty input can force multi-gigabyte allocation and OOM-kill the process. MatchTimeout does not fully mitigate this because the memory is allocated faster than the 100 ms timeout clock can fire. This issue has been patched in version 2.3.0.

Record
CVE-2026-77299
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-400, CWE-770
Updated
2026-11-07
OSVDEBIAN-CVE-2026-77299 7.5

Regexp2 is a feature-rich RegExp engine for Go. Prior to version 2.3.0, when regexp2 compiles and matches a pattern containing a large fixed-count quantifier applied to a zero-width subexpression — e.g. (?:){50000000} — the match engine executes the empty loop body m-1 times, pushing two integers onto the backtracking stack on every iteration. Because the parser accepts any repetition count up to math.MaxInt32 and the backtracking stack grows without bound, a pattern of fewer than 20 bytes matched against an empty input can force multi-gigabyte allocation and OOM-kill the process. MatchTimeout does not fully mitigate this because the memory is allocated faster than the 100 ms timeout clock can fire. This issue has been patched in version 2.3.0.

Record
DEBIAN-CVE-2026-77299
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-07
OSVUBUNTU-CVE-2026-77299 7.5

Regexp2 is a feature-rich RegExp engine for Go. Prior to version 2.3.0, when regexp2 compiles and matches a pattern containing a large fixed-count quantifier applied to a zero-width subexpression — e.g. (?:){50000000} — the match engine executes the empty loop body m-1 times, pushing two integers onto the backtracking stack on every iteration. Because the parser accepts any repetition count up to math.MaxInt32 and the backtracking stack grows without bound, a pattern of fewer than 20 bytes matched against an empty input can force multi-gigabyte allocation and OOM-kill the process. MatchTimeout does not fully mitigate this because the memory is allocated faster than the 100 ms timeout clock can fire. This issue has been patched in version 2.3.0.

Record
UBUNTU-CVE-2026-77299
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-07
OSVAZL-112697 No score

CVE-2026-77299 affecting package regexp 1.5-24

Regexp2 is a feature-rich RegExp engine for Go. Prior to version 2.3.0, when regexp2 compiles and matches a pattern containing a large fixed-count quantifier applied to a zero-width subexpression — e.g. (?:){50000000} — the match engine executes the empty loop body m-1 times, pushing two integers onto the backtracking stack on every iteration. Because the parser accepts any repetition count up to math.MaxInt32 and the backtracking stack grows without bound, a pattern of fewer than 20 bytes matched against an empty input can force multi-gigabyte allocation and OOM-kill the process. MatchTimeout does not fully mitigate this because the memory is allocated faster than the 100 ms timeout clock can fire. This issue has been patched in version 2.3.0.

Record
AZL-112697
Updated
2026-11-06

Affected products

Affected packages

Affected packages
PackageAffectedFixed
regexp
Azure Linux:3
through 1.5-24 None known
golang-github-dlclark-regexp2
Debian:12
All versions, plus listed versions
1.10.0+ds1-11.10.0+ds1-1~bpo12+11.11.0+ds1-11.4.0+ds1-1
None known
golang-github-dlclark-regexp2
Debian:13
All versions, plus listed versions
1.11.0+ds1-1
None known
golang-github-dlclark-regexp2
Debian:14
All versions, plus listed versions
1.11.0+ds1-1
None known
golang-github-dlclark-regexp2
Ubuntu:18.04:LTS
All versions, plus listed versions
1.1.6-1
None known
golang-github-dlclark-regexp2
Ubuntu:20.04:LTS
All versions, plus listed versions
1.1.6-21.2.0-1
None known
golang-github-dlclark-regexp2
Ubuntu:22.04:LTS
All versions, plus listed versions
1.2.0-11.4.0+ds1-1
None known
golang-github-dlclark-regexp2
Ubuntu:24.04:LTS
All versions, plus listed versions
1.4.0+ds1-11.10.0+ds1-1
None known
golang-github-dlclark-regexp2
Ubuntu:26.10
All versions, plus listed versions
1.11.0+ds1-1
None known
golang-github-dlclark-regexp2
Ubuntu:26.04:LTS
All versions, plus listed versions
1.11.0+ds1-1
None known

History

History
RecordedChangedSources
affected, aliases, published, referencesEUVD, NVD, OSV
referencesCVE List
affected, aliases, referencesOSV
affected, aliases, referencesOSV
aliases, referencesNVD, OSV
cwes, references, severity, titleCVE List
first indexedEUVD

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-77299 is a high vulnerability (CVSS 7.5) in Dlclark Regexp2, published November 6, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.35%, the 28th percentile. No source names a fixed version.

References

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